At the soundside edge of Topsail Island, a hole in the ground is not unusual. Marsh grass gives way to higher soil, fiddler crabs disappear when footsteps approach, and small brown crabs move beneath boards, leaves, and anything else that holds a little shade. A burrow at the edge of a coastal yard may belong to an animal that has lived along this shore far longer than the yard has.
That is why a hole alone would be poor evidence of a blue land crab.
The animal itself would be harder to overlook. A mature blue land crab, Cardisoma guanhumi, can grow to nearly six inches across its shell, with legs that make it appear larger still. An adult male is often blue-gray and carries one powerful claw, but females may be pale gray or white, while younger crabs can be orange, brown, or purple. From a distance, the uneven claws can resemble those of a fiddler crab, except the entire animal has been enlarged to a scale unfamiliar in a Carolina backyard (Hostetler et al., 2025).
Until recently, it was also unfamiliar along this part of the coast. The blue land crab’s historically documented range in the continental United States followed the Gulf of Mexico and southern Florida, with Vero Beach long recognized as its northern Atlantic limit (Scott et al., 2023). Occasional South Carolina records began in 2008, followed by 53 verified sightings there during a concentrated period of public reporting in fall 2022 (Scott et al., 2023). North Carolina confirmed its first blue land crab in summer 2023. By August 2026, 23 sightings had been confirmed statewide and another 34 reports remained unverified. Two of the confirmed records this year came from Emerald Isle (NC DEQ, 2026).
Those numbers do not yet describe a population. They describe a question appearing in yards, along roads, and beside the marsh: whether a warm-water crab is occasionally reaching North Carolina or beginning to live here.
A Crab That Does Not Stay in One World
The blue land crab is neither a displaced Atlantic blue crab nor simply a giant fiddler. The shared color and oversized claw describe what it looks like, not its closest relatives. It belongs to Gecarcinidae, the land-crab family, whose members have moved much of adult life above the tide. Their gills still do the breathing, even in air, and those gills must remain damp. The crab can leave the water; it cannot leave water behind (Marin & Tiunov, 2023).
That need for moisture keeps the crab between two worlds. Adults may live above the reach of ordinary tides—in coastal forests, brushy ground, grasslands, drainage edges, and even yards—but they return to damp shelter when the day becomes hot or when a newly molted shell leaves them vulnerable. Many blue land crabs can live near one another without sharing that refuge; each normally keeps a burrow of its own (Herreid & Gifford, 1963; Moraes-Costa & Schwamborn, 2018).
That higher position separates the blue land crab from many crabs living in the flooded marsh below it, but not completely. Its life still returns to the estuary. After mating, a female carries hundreds of thousands of eggs beneath her abdomen and travels to salt or brackish water to release them (Hostetler et al., 2025). The larvae drift through several planktonic stages before settling and returning to land as small crabs. Warm water is particularly important during this development, while salinity determines which parts of an estuary can carry the larvae successfully (Costlow & Bookhout, 1968a, 1968b).
An adult can therefore live beneath shrubs beside a yard while its offspring begin among fishes and plankton. The species belongs to the coastal upland and the estuary at the same time, and that divided life helps explain how an animal tied to one burrow can appear far beyond the range where its adults were previously known.
How a Southern Crab Reached This Shore
Blue land crabs are not likely to have walked from Florida to the Carolinas. Adults forage close to their burrows and show strong attachment to a small home area. Females make longer reproductive movements toward water, but those are local journeys between upland burrows and larval-release sites rather than migrations along hundreds of miles of coastline (Moraes-Costa & Schwamborn, 2018).
Long-distance movement is more plausible during the larval stage. Once released, larvae spend weeks in coastal water before returning to land, allowing currents to carry them beyond the place where they hatched (Hostetler et al., 2023). A widening pattern of sightings from Florida through Georgia and South Carolina would be consistent with natural range expansion as warming water and milder cold periods make northern development and survival more possible (Costlow & Bookhout, 1968b; NC DEQ, 2026; Scott et al., 2023). Human transport, including movement with vessels or materials, remains another possibility because the present records do not yet reveal how the crabs arrived (NC DEQ, 2026).
Warmer conditions in Florida would not simply make the crabs decide to leave. The more relevant change would occur at the northern boundary, where conditions that once killed larvae or prevented overwintering may no longer do so as reliably (Costlow & Bookhout, 1968b). Warming can open habitat ahead of a species without pushing adults out of the habitat behind it.
It is tempting to imagine worsening conditions in Florida sending blue land crabs north, but that does not fit particularly well with how the adults live. Coastal development, altered groundwater, harvesting, and the loss of mangrove-edge habitat have reduced populations in parts of Puerto Rico and Brazil. When the ground around an adult’s burrow is destroyed, however, the crab may move only a short distance or disappear with the habitat. It does not begin a walk to North Carolina (Govender et al., 2008; Moraes-Costa & Schwamborn, 2018).
Development may matter after the much smaller, drifting stage has already reached a new shore. A canal edge, drainage ditch, watered lawn, or patch of coastal vegetation can offer the damp ground a young crab needs as it leaves the estuary. Human-altered places may therefore help connect suitable patches without being the reason the crab traveled north in the first place (Riascos et al., 2024).
So is the blue land crab native to North Carolina, or is it invasive? Neither label fits neatly yet. The species is native to warmer parts of the western Atlantic and Gulf of Mexico, including Florida, but North Carolina lies beyond its historically recognized Atlantic range in the United States. If larvae are reaching the Carolinas on coastal currents and surviving because conditions have become more favorable, then the crab’s natural range may be expanding. If crabs arrived with boats or transported materials, that would be an introduction. The sightings cannot yet tell us which occurred (Scott et al., 2023; NC DEQ, 2026).
Either way, arrival alone does not make a species invasive. The blue land crab would have to establish a reproducing population, continue spreading, and cause ecological or economic harm. North Carolina has confirmed crabs, but it does not yet have evidence of an established, harmful population (NC DEQ, 2026).
Emerald Isle Is Not Far Away
There were two confirmed blue land crab sightings in Emerald Isle this year, out of 23 confirmed cases across North Carolina (NC DEQ, 2026). This is what makes the Emerald Isle records matter here. The confirmed crabs were not found along some distant part of the North Carolina coast. They were found on Bogue Banks, northeast of Onslow County and only several dozen coastal miles from North Topsail Beach.
Between Emerald Isle and Topsail are connected sounds, tidal creeks, inlets, marshes, developed islands, and the Intracoastal Waterway. A crab confirmed on Bogue Banks does not prove that one is already living around North Topsail, Surf City, or the soundside of Topsail Island. It does place the animal within a coastal landscape that continues toward all three.
That does not mean currents are carrying crabs neatly from Emerald Isle toward Topsail, and the statewide sightings should not be read as a marching line. Some animals may represent separate arrivals; others may have gone unnoticed for years. The map brings the question closer. Only repeated observations can show where the crab has actually found a place—and which members of the existing crab community are already there.
The Crabs Already Here
Onslow County’s marsh edge is not waiting empty for a land crab to arrive. Several native crabs divide the same transition from tidal creek to high ground, although each uses a somewhat different part of it.
Comparison of the blue land crab to other crabs seen in our Onslow County area. | Image credit: SC Department of Natural Resources
At low tide, the easiest to notice are often fiddlers. Atlantic marsh fiddler crabs,Minuca pugnax, favor muddier marsh sediment, while Atlantic sand fiddlers,Leptuca pugilator, are more common across sandy flats and the higher portions of the marsh. Red-jointed fiddler crabs,Minuca minax, appear where the water is fresher. Marsh and sand fiddlers have long been documented in North Carolina salt marshes, gathering into the familiar patches that vanish into small holes when a person approaches (O’Connor, 1993).
They sift algae, microbes, and bits of organic material from the surface, leaving tiny feeding marks across exposed sediment. Even a male carrying an oversized claw has a body only a fraction of the width of an adult blue land crab.
Closer to the cordgrass, purple marsh crabs,Sesarma reticulatum, move along muddy creek banks and feed heavily on the grass, including stems and tissues belowground. At ordinary numbers they are part of the marsh’s long-established community. Where their numbers become unusually high, their feeding can strip away vegetation and leave sediment exposed (Bertness et al., 2014; Wittyngham et al., 2024).
At the upper edge, the small brown crab beneath a board or patch of leaves may be a squareback marsh crab,Armases cinereum. Of the native crabs, it is the most likely to meet a blue land crab where marsh gives way to the yard. It moves above the high-water line, sometimes crossing lawns or climbing garage walls, and eats fallen leaves, living plants, and small invertebrates. Its menu is broad in much the same way as a blue land crab’s, although the squareback itself is far smaller (Buck et al., 2003).
Other familiar crabs belong to neighboring settings. Atlantic mud crabs such as Panopeus herbstii remain among oyster shells, rocks, and submerged structure, where their heavy claws open oysters, clams, barnacles, and snails. Ghost crabs,Ocypode quadrata, occupy the open beach and dune sand on the ocean side. Either may be close in geographic distance to a blue land crab, but neither uses the soundside grass-to-yard boundary in quite the same way.
Each of these crabs already belongs to a particular part of the shore. A blue land crab would not arrive in an empty niche, but it would not duplicate any one of them either. To see where the differences matter, we have to look below the opening.
The Architecture Beneath the Opening
For a burrowing crab, the tunnel is more than a hiding place. It is a shelter from heat and predators, a humid chamber that protects the gills, and a safe place to molt. Its shape reflects the problem the crab needs it to solve, which is why burrows built only a few yards apart can belong to very different lives.
A blue land crab begins on higher ground with a comparatively broad entrance, then turns downward toward moisture. There is no single blueprint hidden below it. Burrows examined with a fiber-optic camera in Puerto Rico included short passages that descended at a shallow angle, longer tunnels that leveled before dropping sharply, and deep curves resembling an inverted S. Forked and corkscrew forms occurred less often. The route varied with the site, but the essential destination was usually the same: a humid refuge at or near groundwater, occupied by one crab rather than a colony sharing one chamber (Moraes-Costa & Schwamborn, 2018; Sample & Albrecht, 2016).
The blue land crab’s burrow will begin their entrance with a steep angle that levels off until a sharp downward turn to reach the water table. | Image credit: Sample & Albrecht, 2016
An Atlantic sand fiddler builds at another scale and for another rhythm. Its narrow shaft descends through sand exposed between tides, and a deeper breeding burrow may extend farther than the temporary refuge used while feeding. Across a flat, many small entrances can stand close together because each belongs to a small crab defending little more than the ground immediately around it. Although the shafts provide shelter and moist air, they remain much narrower than the passage required by an adult blue land crab (Christy, 1982). A fiddler opening would therefore be a poor ready-made home for a mature Cardisoma.
A 3D cast and schematic show the burrow formation of an Atlantic fiddler crab. | Image Credit: di Virgilio & Riberio, 2013
The purple marsh crab offers a different contrast. Its burrows occupy muddy, rooted creek banks and can become part of a connected network with several openings. When those networks become dense, especially where vegetation has already thinned, excavation and cordgrass feeding can loosen the bank and make sediment easier for moving water to carry away (Bertness et al., 2014; Farron et al., 2020). A blue land crab generally begins above ordinary tidal flooding and maintains a more solitary route toward groundwater. Its burrow should not be assumed to undercut a creek bank in the same way simply because both animals dig.
A ghost crab may also leave one obvious opening and a mound of newly moved sand, but its address is usually the open ocean beach or foredune. Its sloping or curving refuge is built in loose, comparatively dry beach sand, not at the moist soundside boundary between marsh and yard.
Ghost crab burrow structure from a 3D cast on a sandy beach | Image credit: Shinoda et al., 2019
The squareback marsh crab makes an even clearer distinction. It commonly slips beneath leaves, logs, rocks, boards, and other cover at the upper marsh edge instead of constructing the large groundwater-reaching tunnel associated with an adult blue land crab. Mud crabs and Atlantic blue crabs do not make permanent terrestrial burrows at all. One uses submerged crevices; the other may bury itself temporarily in bottom sediment.
The squareback marsh crab may use rocks, leaves or other surface materials to hide beneath instead of a burrow. | Image credit: critterbliss, iNaturalist
Burrow reuse deserves equal care. Smaller blue land crabs have been found in openings much larger than their bodies, which is consistent with their moving into burrows abandoned by larger blue land crabs (Carmona-Suárez & Guerra-Castro, 2012). For a smaller crab, an empty tunnel would mean less digging, less time exposed aboveground, and immediate access to a refuge that already holds moisture. Those are likely advantages rather than benefits tested directly.
The other crabs along a Carolina shore do not appear to offer the same shortcut. Their shelters are too narrow, too low in the marsh, too dry, or not true burrows at all. Nothing currently shows that blue land crabs routinely take over and enlarge the burrows of another crab species.
The digging leaves more than a hole. Soil brought up from below is spread across the surface, while leaves, scraps of food, old molts, and waste may collect inside. In places where blue land crabs are established, the soil within their burrows differs from the ground beside them in its mixture of sand and silt, acidity, organic matter, and nutrients including nitrogen, magnesium, and potassium (Quintero-Torres et al., 2018).
The open tunnel also allows air and water to reach soil that had been sealed underground. Across many kinds of coastal crabs, burrowing tends to loosen sediment and change the chemical work carried out there by microbes. How much changes—and whether the effect helps or harms the plants above—depends upon the crab, the vegetation, and where the burrow sits (Rinehart et al., 2024).
Water salinity is shown in a burrowed marsh (a), a straight burrowed marsh (b), a sloped marsh (c ), and a marsh at the high tide stage and how salinity is distributed in the marsh as influenced by burrows. | Image credit: Yin et al., 2023
That does not mean each hole ventilates an entire marsh. Oxygen entering a tunnel may change only a thin layer of soil along its walls. Around fiddler burrows, that reach has been far smaller than the familiar phrase “aerates the soil” might suggest (Michaels & Zieman, 2013). A single high-ground blue land crab tunnel is not a new tidal creek either. Rain, groundwater, or an unusually high tide may enter it and change the wetness immediately around the opening, but blue land crab burrows have not been shown to redirect tidal flow through a maritime forest.
Roots present the same uncertainty. Digging can break fine roots and loosen the soil holding them, while the extra space and shifted nutrients around a tunnel may create new conditions for roots and soil life. Blue land crabs also clip and eat plants aboveground, so a damaged plant would not tell us whether feeding, digging, or both were responsible.
One occupied hole may change little beyond a small patch of ground. If the same digging were repeated across many burrows, those patches could begin to influence which plants take hold, how firmly their roots bind the edge, and how water moves through the soil. That possibility is one reason burrows are worth mapping. It is not evidence that those changes are already happening at North Carolina sighting sites.
At first, the tunnel keeps one crab alive. Only when that work is repeated across a place does it begin to become part of the landscape.
From the surface, however, most of that architecture remains hidden.
What a Burrow Can—and Cannot—Tell Us
A mature blue land crab may leave an opening three to five inches wide. Freshly excavated soil may collect around the entrance, and plant pieces or tracks may be visible nearby. These clues become more persuasive when the hole sits above normal tidal flooding in shaded, moist ground and a very large crab has been seen retreating into it (Hostetler et al., 2025).
It is still not an identification. A smaller blue land crab may occupy an older, larger burrow, while erosion can widen the entrance to a much smaller tunnel. Marsh soil also collapses, roots leave openings, rodents dig, and water continually reshapes the grass line. Size alone can mislead, particularly in a photograph with nothing nearby for scale.
The setting and the pattern offer better clues. Many small holes spread across exposed mud or sand point toward fiddlers. Several openings cut through a rooted creek bank fit purple marsh crabs. One hole high on the dry ocean beach is more likely a ghost crab’s. Squarebacks are often found beneath something rather than beside a large mound of freshly dug soil. The strongest match for the blue land crab would bring several details together: a broad opening on higher soundside ground, signs of recent digging, and a crab far larger than the native marsh species.
That is why a useful photograph includes more than the hole. The crab, entrance, moved soil, surrounding plants, nearby water, and something familiar for scale allow the scene to be read together. There is no need to dig, probe, or flood the tunnel. Without the animal, a burrow can identify a place worth watching, but not the species living beneath it.
What the New Crab Would Eat
The large claw may make a blue land crab look like a hunter arriving to eat every smaller crab in its path. Most of what it gathers, however, is plant material: fallen leaves, fruit, berries, flowers, tender shoots, grasses, and seeds. It may carry that food home and pull some of it underground. Insects, carrion, feces, and other animal matter add to the diet when available, and blue land crabs sometimes eat one another (Gifford, 1962; Herreid, 1963; Moraes-Costa & Schwamborn, 2018).
That does not place native crabs entirely off the menu. A blue land crab may seize a small animal it can catch, but regular hunting of fiddlers, squarebacks, or purple marsh crabs is unlikely to be its main influence. The more important changes would probably begin with the plants and fallen leaves it removes, the ground it excavates, and the space it keeps around its burrow.
The amount of competition would differ from crab to crab. Fiddlers graze the thin film of algae, microbes, and organic particles coating the marsh surface, so they share relatively little food with a crab gathering fruit and leaves above the high-tide line. Squareback and purple marsh crabs share more of that plant-based menu, although they forage at different scales and in different parts of the marsh. If blue land crabs remain, the strongest overlap may be over shaded ground, damp refuge, and nearby plant food rather than over a particular prey animal.
What Established Populations Tell Us
Sharing food and high ground does not make displacement inevitable. Where blue land crabs have lived for generations, other crabs continue to live beside them by using different levels of the shore. Along the Brazilian coast, for example, the mangrove crab,Ucides cordatus, digs into softer ground between the tides, while Cardisoma lives higher in firmer, sandier soil. Their ranges overlap without their burrows occupying precisely the same ground (Firmo et al., 2012).
North Carolina has a different community, but the same separation by water, soil, and elevation is already familiar here. The squareback comes closest to overlapping with a blue land crab at the upper edge. Even there, one defended Cardisoma burrow might cost a squareback a feeding spot without removing squarebacks from the wider marsh.
The first change people noticed might therefore be simpler than one crab replacing another: a much larger animal at the grass line, fresh soil beside an entrance, fallen fruit or leaves drawn toward it, and tender plants clipped within a short walk of the burrow.
That picture could change if the crabs became numerous. Many defended burrows would divide more of the narrow band of damp high ground, increasing competition for shelter and food. Their digging would repeat the small soil changes described above, while their feeding could influence which seeds and seedlings survive and how quickly fallen leaves disappear. Those broader forest effects are known across several land-crab species rather than from a newly established Cardisoma population, but they show why abundance matters more than the mere arrival of one large crab (Lindquist et al., 2009).
Predators would respond only if the crabs became dependable prey. Large birds and mammals eat blue land crabs within their established range, while eggs and larvae released into the estuary become food for aquatic animals (Firmo et al., 2012; Hostetler et al., 2025). One adult crossing a Carolina yard offers one unusual meal. A recurring population could give raccoons or coastal birds a reason to search the marsh edge and could place many larvae into the estuarine food web.
This is where two kinds of change can look like the same thing. Digging alters the ground directly, making the crab an ecosystem engineer (Rinehart et al., 2024). A trophic cascade would have to continue through feeding relationships: fewer surviving seedlings changing the vegetation, for example, or predators drawn to land crabs changing their pressure on other prey (Lindquist et al., 2009).
Blue land crabs are capable of beginning both pathways. What the North Carolina sightings cannot yet tell us is whether enough crabs are arriving, surviving, and reproducing for the work of individuals to become the work of a population.
When One Sighting Becomes a Place
One dated photograph gives the map a place. Another observation weeks or months later begins to show whether the crab stayed. As those records accumulate, they can reveal when the crabs are active, whether they appear after rain, which kinds of ground they use, and whether they return across seasons. Crabs of different sizes at one site may have survived across more than one year, while juveniles, egg-bearing females, or repeated movements toward the water would offer stronger evidence that the species is completing more of its life cycle here.
The same map can show where the larger ecological questions belong. One wandering adult does not tell us that native crabs are being displaced or that a trophic cascade has begun. Several occupied burrows, plant damage, younger crabs, and repeated sightings at the same place would give biologists a reason to compare its vegetation, soil, native crabs, and predators with nearby places where Cardisoma is absent.
Anyone who sees a possible blue land crab can photograph it from a safe distance and submit the image, date, and location through the Blue Land Crab Sightings reporting. A photograph showing the animal, its approximate scale, and the surrounding habitat is more useful than trying to catch or relocate it.
That distinction matters for anyone standing at the grass line. A three-inch hole is not an identification, clipped leaves are not proof of ecological harm, and a large crab is not automatically an invasive species. Each is a piece of context. Together, photographed and reported without catching or relocating the animal, those pieces can show whether North Carolina is receiving occasional southern visitors or adding a new resident to the narrow landscape between the forest and the sea.
The coast will answer that slowly, one place at a time.
References
Bertness, M. D., Brisson, C. P., Bevil, M. C., & Crotty, S. M. (2014). Herbivory drives the spread of salt marsh die-off. PLoS ONE, 9(3), e92916. https://doi.org/10.1371/journal.pone.0092916
Buck, T. L., Breed, G. A., Pennings, S. C., Chase, M. E., Zimmer, M., & Carefoot, T. H. (2003). Diet choice in an omnivorous salt-marsh crab: Different food types, body size, and habitat complexity. Journal of Experimental Marine Biology and Ecology, 292(1), 103-116. https://doi.org/10.1016/s0022-0981(03)00146-1
Carmona-Suárez, C. A., & Guerra-Castro, E. (2015). Comparison of three quick methods to estimate crab size in the land crabs <i>Cardisoma guanhumi</i> Latreille, 1825 and <i>Ucides cordatus</i> (Crustacea: Brachyura: Gecarcinidae and Ucididae). Revista de Biología Tropical, 60, 139. https://doi.org/10.15517/rbt.v60i0.19854
Costlow, Jr., J. D., & Bookhout, C. G. (1968a). The complete larval development of the land-crab, Cardisoma guanhumi Latreille in the laboratory (Brachyura, Gecarcinidae). Crustaceana, 15(3), 259-270.
Costlow, Jr., J. D., & Bookhout, C. G. (1968b). The effect of environmental factors on development of the land-grab,cardisoma guanhumiLatreille. American Zoologist, 8(3), 399-410. https://doi.org/10.1093/icb/8.3.399
Farron, S., Hughes, Z., FitzGerald, D., & Strom, K. (2020). The impacts of bioturbation by common marsh crabs on sediment erodibility: A laboratory flume investigation. Estuarine, Coastal and Shelf Science, 238, 106710. https://doi.org/10.1016/j.ecss.2020.106710
Firmo, A., Tognella, M. M., Silva, S. R., Barboza, R. R., & Alves, R. (2012). Capture and commercialization of blue land crabs (“guaiamum”) Cardisoma guanhumi (Lattreille, 1825) along the coast of Bahia state, Brazil: An ethnoecological approach. Journal of Ethnobiology and Ethnomedicine, 8(1). https://doi.org/10.1186/1746-4269-8-12
Gifford, C. A. (1962). Some observations on the general biology of the land crab, cardisoma guanhumi (Latreille), in South Florida. The Biological Bulletin, 123(1), 207-223. https://doi.org/10.2307/1539516
Govender, Y., Sabat, A. M., & Cuevas, E. (2008). Effects of land-use/land-cover changes on land crab,Cardisoma guanhumi, abundance in Puerto Rico. Journal of Tropical Ecology, 24(4), 417-423. https://doi.org/10.1017/s0266467408005130
Herreid, C. F. (1963). Observations on the feeding behavior of Cardisoma Guanhumi (Latreille) in southern Florida1). Crustaceana, 5(3), 176-180. https://doi.org/10.1163/156854063×00093
Herreid, C. F., & Gifford, C. A. (1963). The burrow habitat of the land crab, Cardisoma guanhumi (Latreille). Ecology, 44(4), 773-775. https://doi.org/10.2307/1933027
Hostetler, M. E., Mazzottii, F. J., & Taylor, A. K. (2025, October 28). Blue land crab (Cardisoma guanhumi) (WEC 30). Department of Wildlife Ecology and Conservation, UF/IFAS Extension. https://ask.ifas.ufl.edu/publication/UW013
Lindquist, E. S., Krauss, K. W., Green, P. T., O’Dowd, D. J., Sherman, P. M., & Smith, T. J. (2009). Land crabs as key drivers in tropical coastal forest recruitment. Biological Reviews, 84(2), 203-223. https://doi.org/10.1111/j.1469-185x.2008.00070.x
Marin, I. N., & Tiunov, A. V. (2023). Terrestrial crustaceans (Arthropoda, crustacea): Taxonomic diversity, terrestrial adaptations, and ecological functions. ZooKeys, 1169, 95-162. https://doi.org/10.3897/zookeys.1169.97812
Michaels, R. E., & Zieman, J. C. (2013). Fiddler crab (Uca spp.) burrows have little effect on surrounding sediment oxygen concentrations. Journal of Experimental Marine Biology and Ecology, 448, 104-113. https://doi.org/10.1016/j.jembe.2013.06.020
Moraes-Costa, D., & Schwamborn, R. (2018). Site fidelity and population structure of blue land crabs (Cardisoma guanhumi Latreille, 1825) in a restricted-access mangrove area, analyzed using PIT tags. Helgoland Marine Research, 72(1). https://doi.org/10.1186/s10152-017-0504-0
O’Connor, N. (1993). Settlement and recruitment of the fiddler crabs Uca pugnax and U. pugilator in a North Carolina, USA; salt marsh. Marine Ecology Progress Series, 93, 227-234. https://doi.org/10.3354/meps093227
Quintero-Torres, E., Chacón, N., & López-Sánchez, B. (2018). The ecosystem engineering role of the neotropical crab Cardisoma guanhumi on mangrove soil properties. Wetlands Ecology and Management, 26(5), 993-1000. https://doi.org/10.1007/s11273-018-9618-7
Riascos, J. M., Obonaga, L. D., & Ramos, J. (2024). Is the threatened land crab Cardisoma guanhumi conquering human‐dominated systems? Ecology and Evolution, 14(4). https://doi.org/10.1002/ece3.10737
Rinehart, S. A., Dybiec, J. M., Walker, J. B., Simpson, L., & Cherry, J. A. (2024). Effects of burrowing crabs on coastal sediments and their functions: A systematic meta‐analysis. Ecosphere, 15(7). https://doi.org/10.1002/ecs2.4927
Sample, S., & Albrecht, M. (2016). Determination of the burrow shapes of Cardisoma guanhumi on Vieques, Puerto Rico. Journal of Coastal Life Medicine, 4(2), 94-97. https://doi.org/10.12980/jclm.4.2016j5-245
Scott, E., Kendrick, M., Kingsley-Smith, P., James, M., Lemeris, J., Weeks, E., & Sasson, D. (2023). Using public sightings to document the widespread distribution of the non-endemic blue land crab, Cardisoma guanhumi, in South Carolina. Southeastern Naturalist, 22(4). https://doi.org/10.1656/058.022.0403
Wittyngham, S. S., Johnson, D. S., Chen, Y., & Kirwan, M. L. (2024). A grazing crab drives saltmarsh carbon storage and recovery. Ecology, 105(9). https://doi.org/10.1002/ecy.4385
Late August does not look much like fall along the Onslow County coast.
The sand is still hot. Afternoon thunderstorms still build over the mainland. The ocean can remain warm enough that stepping into it hardly feels like relief.
But beneath the surface, fall has already begun.
Fish that spent summer scattered through sounds, creeks, reefs, and nearshore water begin gathering. Shrimp start working their way out of nursery creeks. Mature female blue crabs move toward saltier water. Schools of mullet begin appearing along the beaches. Sharks that spent the warmer months farther north or inside coastal waters begin shifting south or offshore.
Above them, the birds begin changing too.
Some are preparing to leave. Others are arriving from places hundreds or thousands of miles away. Still others simply become more noticeable because suddenly there is food everywhere.
What looks from shore like a few gulls working over the water, a school of baitfish flashing beside a pier, or pelicans repeatedly diving beyond the breakers is part of something much larger.
For a few months each fall, the food web itself begins to move.
When the Water Begins to Change
Animals do not wait for a date on the calendar. Along the coast, fall arrives through changes in water temperature and daylight, but also through salinity, currents, rainfall, food availability, and the timing of reproduction. Different species respond to different combinations of those signals, which means the seasonal movement beginning beneath the surface is not one migration triggered in one way.
For some animals, cooling water begins narrowing where they can comfortably remain. King mackerel (Scomberomorus cavalla) favor warm coastal water and become less common as temperatures fall much below about 68°F, while cobia (Rachycentron canadum) begin leaving northern summer habitats as water cools through roughly the same range. Spotted seatrout (Cynoscion nebulosus) respond differently. Rather than leaving our estuaries altogether, they begin shifting toward creeks, channels, and deeper water where a few additional feet of depth can provide protection from the colder temperatures still to come (North Carolina Division of Marine Fisheries, 2022; Jensen & Graves, 2020; Ellis, Buckel, & Hightower, 2017; Ellis, Buckel, Hightower, & Poland, 2017).
King mackerel (Scomberomorus cavalla), a warm-water coastal fish that becomes less common as fall temperatures drop. | Image credit: Sylvain Le Bris, iNaturalist
Temperature can work together with another signal that changes every year whether the weather feels like fall or not: shortening daylight. Blacktip and sandbar sharks moving along the western Atlantic begin their southward migration as sea-surface temperatures change and the days grow shorter, leaving northern and Mid-Atlantic summer habitats and gradually shifting toward the South Atlantic Bight and Florida for winter and spring (Manz et al., 2025).
For other animals, autumn movement is tied less to escaping cooling water than to reaching the next stage of their life cycle. Southern flounder (Paralichthys lethostigma) spend their first years in estuarine waters, where shallow sounds, rivers, and creeks provide nursery and feeding habitat. Females begin maturing surprisingly early: some are reproductively mature by age one, most by age two, and nearly all by age three. Immature fish can remain within the estuary through winter, but once mature, southern flounder begin joining the fall movement through the inlets and toward offshore spawning grounds (Midway & Scharf, 2012; Craig et al., 2015).
That means fish of different ages can occupy the same estuary through summer and then take different paths as fall develops. A young flounder may remain behind while an older fish that spent the season feeding in the same system begins moving toward the ocean.
So while late-August water may still feel thoroughly summerlike to someone standing waist-deep at Topsail, the animals beneath the surface are already responding to a season that is only beginning to become visible above it.
One of the first clues may simply be a fish jumping beside you.
The Mullet Begin to Run
Striped, or sea, mullet (Mugil cephalus) spend much of the warmer season feeding throughout estuaries, sounds, tidal creeks, and protected coastal waters. By late summer, however, their movements begin to change. In North Carolina, striped mullet travel most actively between August and November as mature fish leave rivers, sounds, and tidal creeks for marine spawning habitat. Their journey carries them through the inlets and offshore into the South Atlantic Bight, with spawning habitat extending from nearshore waters toward the outer continental shelf where shelf water meets the influence of the Gulf Stream (Bacheler et al., 2005). For fish that spent the summer inside an estuary, that is a considerable change in geography, but still a relatively regional migration compared with species that will later continue much farther south along the Atlantic coast.
They begin making that seasonal journey relatively young. About half of North Carolina striped mullet are reproductively mature by age one, although maturity varies among individuals, and older adults may return to estuarine habitats after spawning. Rather than leaving the estuary permanently as they mature, they move between estuarine feeding grounds and marine spawning habitat as part of a seasonal cycle (Bichy, 2004; Bacheler et al., 2005).
For beachgoers, this can become one of the easiest fall migrations to notice. Fish that spent summer spread through rivers, creeks, and sounds begin collecting into increasingly conspicuous schools as they move toward inlets and coastal water. Once along the ocean beach, dense schools may travel remarkably close to shore, sometimes darkening the shallows or stretching along the surf zone beyond what can be seen from one spot. Mullet are frequent jumpers as well, so a school may first reveal itself as silver fish repeatedly breaking the surface. By the time those schools reach the inlet and beach, they are carrying more than themselves with them. Striped mullet feed low in the food web, consuming algae, detritus, and organic material associated with estuarine sediments. As thousands of them move out of the estuary, that stored production moves with them and becomes available to the larger fishes, sharks, and birds that feed along the coast (Bacheler et al., 2005).
Those predators are already moving through the same corridor. Bluefish (Pomatomus saltatrix) feed heavily on schooling fishes such as mullet, menhaden, and silversides. Spanish mackerel (Scomberomorus maculatus) work schools of anchovies and other small baitfish, while blacktip sharks (Carcharhinus limbatus) and spinner sharks (Carcharhinus brevipinna) take advantage of dense concentrations of coastal prey.
The fall mullet run is therefore more than thousands of fish leaving an estuary. It is estuarine production moving through the inlet and onto the beach, where it begins to intersect with predators following their own seasonal routes.
That intersection is what makes the migration suddenly visible. A school that might otherwise pass unnoticed can tighten near shore as bluefish, mackerel, sharks, and birds begin responding to the same moving concentration of prey.
Spanish Mackerel, Bluefish, and the Surface Chase
Sometimes the easiest way to find a migration is not to look for the animals themselves, but for what happens to the water when they arrive.
Spanish mackerel (Scomberomorus maculatus) spend the warmer months moving north along the Atlantic coast, reaching North Carolina in spring and remaining through summer and early fall while coastal water stays above roughly 68°F. As that warm-water window begins closing, they turn south again toward winter habitat off Florida, feeding heavily along the way on anchovies, silversides, menhaden, mullet, and other small schooling fishes (North Carolina Division of Marine Fisheries, 2026; Sutherland & Fable, 1980).
Spanish mackerel (Scomberomorus maculatus) traveling in a dense school. | Image credit: Shutterstock
Bluefish (Pomatomus saltatrix) are moving through the same changing coast, but their fall pattern varies with age. Smaller bluefish tend to migrate south along the shoreline as water cools, while larger adults make more of an inshore-to-offshore shift. Farther north, fall movement begins as water drops into roughly the mid-50s Fahrenheit, gradually carrying fish into the warmer coastal waters to the south (Lund & Maltezos, 1970). By the time those movements reach the Carolina coast, they are crossing water already crowded with prey. Anchovies, silversides, juvenile menhaden, and other tiny schooling fishes—many of the fishes beachgoers collectively call “glass minnows”—can become compressed near the surface, and even wash onto shore, as mackerel and bluefish strike through the schools from below.
Little tunny (Euthynnus alletteratus), better known locally as false albacore, can join that fall activity around inlets and nearshore waters as well. They too make seasonal movements along the Atlantic coast, shifting north through the warmer part of the year and south again through fall and winter while feeding in fast-moving schools (North Carolina Division of Marine Fisheries, 2026).
Little tunny (Euthynnus alletteratus), also known as false albacore, moving in a feeding school. | Image credit: aurelpap, iNaturalist
From the beach, separating one predator from another may be nearly impossible. What becomes visible instead is the chase. A patch of otherwise smooth ocean suddenly begins to boil as tiny fish scatter across the surface. Gulls and terns converge overhead, pelicans turn toward the commotion, and dark backs or silver flashes cut through the school below.
Sometimes the entire event moves several hundred yards down the beach within minutes.
And the animals doing the chasing are still part of the food web themselves. Spanish mackerel and bluefish may be predators here, but both can become prey for larger sharks and tunas farther up the same moving chain. A small fish feeding on plankton becomes food for a mackerel; that mackerel may later become food for a shark.
Fall has compressed several levels of the food web into the same patch of water, and for a few minutes the whole thing becomes visible from shore.
The Sharks Following Fall
Shark migration can sound dramatic because sharks are dramatic animals.
Ecologically, however, their fall movements make perfect sense. Food is moving, water temperature is changing, nursery seasons are ending, and remaining in shallow water becomes increasingly expensive for animals whose body temperature largely follows the environment around them.
Blacktip sharks (Carcharhinus limbatus) and spinner sharks (Carcharhinus brevipinna) are warm-water coastal sharks frequently associated with schools of mullet, menhaden, and other fishes.
Blacktip (Carcharhinus limbatus) and spinner sharks (Carcharhinus brevipinna) can look very similar; fin markings and body proportions help separate the two. | Image credit: Bowers & Kaijiura, 2023
As coastal waters cool, these highly mobile sharks begin shifting south. For blacktips, that can mean a substantial journey: sharks that spent the warmer months along the Carolinas and farther north move down the Atlantic coast toward Florida, with large winter aggregations forming in the warm coastal waters of southeast Florida. Spinner sharks also shift south as autumn progresses, although exactly how their seasonal routes connect Carolina summer habitat with winter habitat farther south is less clearly understood (Manz et al., 2025). Their movement is not caused by prey alone. Temperature and the gradually shortening length of the day contribute to the timing of autumn migration, while concentrations of prey can influence where sharks pause and feed along the route (Manz et al., 2025). That shortening daylight is the actual span between sunrise and sunset—not the hour shown on our clocks. The gradual loss of daylight from late summer into fall provides a predictable seasonal signal even when water temperatures vary from one year to the next.
The shallow coastal habitats these sharks use during migration are also important much earlier in life. Blacktip pups are born in protected nursery areas away from most adults, and young sharks can remain associated with shallow coastal habitat for several years as they grow. Males generally reach maturity around four to five years old, while females mature closer to six or seven; spinner sharks follow a similarly slow timetable, with females maturing later than males (Carlson et al., 2006; NOAA Fisheries, 2017).
That means the shallow water along the coast is not simply a birthplace young sharks immediately leave behind. It can remain part of their world through several juvenile years before the broader seasonal movements of adulthood become established. Exactly how strongly young sharks remain connected to individual nursery areas is still being studied, but nursery habitat can shape where they spend some of the most vulnerable years of their lives (Heupel et al., 2007; NOAA Fisheries, 2017, 2024).
Around New River Inlet and the beaches of Topsail, those later seasonal movements begin intersecting with the migrations already underway. Schools of mullet, Spanish mackerel, and other coastal fishes can create concentrated feeding opportunities along the same corridor, and both blacktips and spinner sharks may breach during fast pursuits, with spinner sharks sometimes twisting through the air in the leaps that gave the species its name (Bangley, 2014).
A beachgoer watching a fall bait ball may therefore be seeing several stages of the coastal food web converge in the same narrow stretch of water.
Atlantic sharpnose sharks (Rhizoprionodon terraenovae) use shallow coastal waters, sounds, bays, and estuaries throughout the warmer months. Adults are generally only a few feet long and feed on small fishes, shrimp, crabs, squid, and other coastal prey (Bethea et al., 2006; Roskar et al., 2024).
Their fall movement is much smaller in scale than the southward migration of blacktips. During summer, Atlantic sharpnose are abundant in the shallow nearshore waters of Onslow Bay, where both immature and mature sharks occur and pups are likely born. As autumn progresses, they become less common in those shallow areas and shift toward deeper coastal habitat. Adults have even been found using offshore wrecks in North Carolina during winter before returning toward shallower water in spring (Roskar et al., 2024).
So for Atlantic sharpnose, fall may mean moving offshore without leaving the region entirely. Predation does not disappear from the coastal food web; it simply shifts into a different part of it.
Atlantic sharpnose shark (Rhizoprionodon terraenovae), a small coastal shark common in North Carolina’s warmer months. | Image credit: Virginia Institute of Marine Science
Sandbar sharks (Carcharhinus plumbeus) show how different that scale can become. Young sandbars spend the warmer months in shallow nursery habitat farther north along the Mid-Atlantic, then move offshore and south during late September and October. Many repeat that seasonal route for several years as juveniles, wintering from North Carolina toward Florida before returning north in spring. As they grow, the journey expands, with older sandbars ranging from southern New England to Florida and Cuba (Merson & Pratt, 2001; McCandless et al., 2007; Kohler et al., 1998).
Their autumn departure is tied closely to cooling water and shortening day length, while prey encountered along the route determines where they may stop and feed (Manz et al., 2025).
Sandbar sharks (Carcharhinus plumbeus), a large coastal species that shifts south and offshore as fall progresses. | Image credit: Simon Peggs, iNaturalist
Off Onslow County, artificial reefs and natural hard-bottom habitats add patches of structure to that broader migration corridor. AR-342, the Onslow Bay Saltwater Fishing Club Reef, lies in about 49 feet of water and is one such patch where fishes and other prey can concentrate along the shelf (North Carolina Division of Marine Fisheries, 2017).
A reef does not have to be an animal’s destination to matter. Sometimes it is simply a place to feed before the migration continues.
AR-342, the Onslow Bay Saltwater Fishing Club Reef, shown within the nearshore reef network off Onslow County. | Image credit: NC Division of Marine Fisheries
Cobia and the Last Warm-Water Feeding
Cobia (Rachycentron canadum) are another warm-season visitor beginning to run out of time. During spring and summer they move north along the Atlantic coast, using coastal and offshore waters from the Carolinas into Chesapeake Bay and farther north. They favor warm water, generally around 68–86°F, and as autumn temperatures begin slipping toward the lower end of that range, they start shifting offshore and south toward warmer winter habitat (Jensen & Graves, 2020).
Cobia (Rachycentron canadum), a warm-water coastal fish that begins shifting offshore and south as autumn temperatures cool. | Image credit: georgeh04, iNaturalist
That places coastal North Carolina somewhere in the middle of the journey. The cobia moving through our waters are not necessarily arriving for winter or leaving from a summer home here.
For many, this stretch of coast is part of the route between the two.
Along the way, structure matters. Buoys, wrecks, reefs, and artificial reefs can gather baitfish and other prey into small pockets of activity in otherwise open water, giving a traveling cobia a place to feed before continuing south (Jensen & Graves, 2020). A reef that holds feeding cobia may also be busy with reef fishes, passing mackerel, schools of bait, and other predators using the same patch of water for their own reasons.
By fall, the coast begins to feel less like a collection of separate habitats and more like a series of connected stopping places along the migration route.
Flounder Leave Through the Bottom
Not every migration announces itself at the surface. Some of the most important fall movement in Onslow County happens quietly along the bottom.
Southern (left) and summer flounder (right) both spend much of their early lives over shallow estuarine and coastal bottoms before mature fish move offshore to spawn. | Image credits: J. Weferling, iNaturalist (left); harrier, iNaturalist (right)
Southern flounder (Paralichthys lethostigma) spend the first years of their lives inside estuaries, lying over mud, sand, oyster habitat, creek bottoms, and other shallow nursery and feeding areas where they prey on fish and crustaceans. In North Carolina, many females begin reaching reproductive maturity around ages one to two and roughly 16 inches in length, although growth and maturity vary considerably among individual fish (Midway & Scharf, 2012). That means a southern flounder can spend years growing within the estuary before ever contributing to the offshore spawning population. Immature fish may remain within estuarine waters through winter, while mature fish begin leaving in fall for offshore spawning habitat. Fish encountered farther offshore tend to be larger and older, while younger fish remain more closely associated with the sounds, rivers, and creeks where they grew (Craig et al., 2015). A fish that spent its first years nearly invisible beneath New River mud can suddenly become part of an offshore migration.
Summer flounder (Paralichthys dentatus) make a similar outward journey, although their early life follows a slightly different timetable. Larvae and juveniles use coastal bays, sounds, and estuaries as nursery habitat for roughly their first 18 to 20 months, and most reach reproductive maturity around age two to three. In the South Atlantic Bight, about half are mature by roughly 11 to 12 inches total length, although females generally mature at a somewhat larger size than males (Packer, 1999).
Like southern flounder, they spend their younger years feeding and growing in protected coastal habitat before mature fish begin moving offshore in fall toward continental-shelf spawning grounds. By then, the fish leaving the estuary are not simply larger versions of the juveniles that remain behind; they are the part of the population capable of producing the next generation. So the two flatfish a beachgoer might easily confuse are doing something remarkably similar at this time of year. Both spend their younger years in shallow coastal and estuarine nursery habitat, and both eventually move offshore to spawn. What differs is the timing—how quickly they mature, how long they remain closely tied to those nursery grounds, and where along the coast each species is most concentrated.
The Fall Runs Gather Nearshore
The familiar fishes around piers change with fall too.
Spot (Leiostomus xanthurus) and Atlantic croaker (Micropogonias undulatus) spend important parts of their early lives inside estuaries, feeding over sandy and muddy bottoms on worms, small crustaceans, organic material, and other small prey (Warlen & Burke, 1990; Ross, 1988)
Atlantic croaker (Micropogonias undulatus) and spot (Leiostomus xanthurus), two familiar estuarine fishes that move toward coastal spawning waters in fall. | Image credit: C. Dzbanski
Spot remain closely tied to estuarine nursery habitat through their first year, gradually moving into deeper and saltier parts of the system as they grow. By fall, the larger fish begin gathering closer to channels, inlets, and the ocean before continuing toward offshore spawning grounds south of Cape Hatteras. There, spawning continues through fall and winter in substantially warmer shelf water, roughly 63–77°F, with the strongest activity around 68°F (Warlen & Chester, 1985; Allen et al., 2024).
Atlantic croaker follow a similar route on a slightly different schedule. Young croaker enter low-salinity estuarine nursery areas after being spawned offshore, then grow rapidly through their first year. As fall develops, many begin moving back toward open coastal water, with the spawning migration beginning as early as September and continuing into winter (White & Chittenden, 1977; Norcross & Austin, 1988).
Weakfish (Cynoscion regalis) join that same seasonal pull toward the coast. Through spring and summer they use sounds, estuaries, and nearshore habitat, feeding heavily on shrimp, crustaceans, and smaller fishes. As autumn water cools toward about 75°F, they begin gathering and shifting offshore and south; during warmer years, some linger longer before making that move (Krause et al., 2020).
Weakfish (Cynoscion regalis), a fall migrant along the Atlantic coast and currently listed as Endangered on the IUCN Red List. | Image credit: aiden007, iNaturalist
By this point in fall, fishes that spent summer scattered through different parts of the estuary are beginning to converge along the same channels, inlets, and nearshore corridor. The movement is outward, but not entirely.
While larger spot and croaker are leaving for offshore spawning grounds, their next generation is already beginning the opposite journey. Larvae produced offshore in fall and winter can begin entering North Carolina estuaries by late fall and early winter, with that inward movement continuing through spring (Warlen & Burke, 1990; Allen et al., 2024).
So even as one generation moves out through the inlet, another is beginning to come back in.
The Fish That Stay—but Change Address
Migration does not always mean leaving Onslow County. For some fishes, fall means finding a different part of the same estuary.
Spotted seatrout (Cynoscion nebulosus), or speckled trout, remain in coastal North Carolina through winter, but they do not necessarily stay where they spent August. As the shallow sounds and creek edges cool, trout begin gathering around channels, deeper holes, creek mouths, and other places where a few extra feet of water can provide more stable temperatures.
Spotted seatrout (Cynoscion nebulosus) moving through shallow coastal water before shifting toward deeper winter habitat as temperatures fall. | Image credit: charliew82, iNaturalist
That difference becomes increasingly important as winter approaches. Spotted seatrout begin showing cold stress when water falls below about 45°F, and prolonged periods below roughly 44.6°F can produce substantial winter mortality in North Carolina. Deeper sections of an estuary can remain slightly warmer during a severe cold event, giving fish somewhere to retreat when the shallows become too cold (Ellis, Buckel, & Hightower, 2017; Ellis, Buckel, Hightower, & Poland, 2017).
So the autumn congregation of trout around creek mouths, bridge structure, channels, and deep holes is more than a change in where they happen to be feeding. By fall, they are beginning to settle into the parts of the estuary that may carry them through winter.
Black drum (Pogonias cromis) reorganize themselves through fall as well, although their movement depends partly on age. Young black drum spend their first year within estuaries, feeding over mud, sand, oyster habitat, and other bottoms rich in worms, small crustaceans, and mollusks. As they grow, they begin using saltier water and deeper coastal habitat, while larger fish are often associated with oyster bars, bridge and dock pilings, channels, and other structure where clams, oysters, crabs, and other bottom prey collect (North Carolina Division of Marine Fisheries, 2026).
Black drum (Pogonias cromis) use estuaries when young, then shift toward deeper, saltier water as they grow and fall progresses. | Image credit: zachs, iNaturalist
By late fall, black drum generally shift away from the shallowest summer habitat toward deeper bays, sounds, channels, and offshore water. Unlike spotted seatrout, there is not one well-defined temperature at which that movement begins. Instead, cooling water gradually changes where suitable feeding and winter habitat remain available, with older fish tending to range farther toward high-salinity and offshore waters (North Carolina Division of Marine Fisheries, 2026).
A piling or oyster bar that held one mix of fishes through summer may still be occupied in November, but by a different combination of animals using the same structure for colder-water feeding and refuge.
The habitat has not disappeared. Its seasonal community has changed.
Shrimp Begin Pouring Out of the Creeks
Some of the most important migrants along the Onslow County coast are only a few inches long.
White shrimp (Litopenaeus setiferus), locally called greentails, spend much of their early lives inside estuarine nursery habitat. They grow rapidly in warm water, and once they reach only about 0.8 to 1.2 inches long, they begin leaving the shallowest marsh habitat for deeper creeks, rivers, bays, and sounds. By late summer and fall, larger young shrimp—often around 4.7 inches or more—are moving farther downstream toward channels, inlets, and ultimately the ocean (North Carolina Division of Marine Fisheries, 2023).
White shrimp (Litopenaeus setiferus) grow quickly in estuarine nurseries before moving downstream toward sounds, inlets, and coastal water in late summer and fall. | Image credit: portulaca, iNaturalist
Cooling water helps drive that progression, but rainfall can accelerate it. Heavy freshwater input lowers estuarine salinity and can push shrimp downstream and toward the ocean before they otherwise would have left. That means a wet fall and a dry fall do not necessarily produce the same migration (North Carolina Division of Marine Fisheries, 2023).
The shrimp are responding to an estuary that is changing around them, and almost everything seems interested in eating them. Flounder, speckled trout, red drum, weakfish, sharks, wading birds, and humans all take advantage of shrimp as they move through the coastal food web (North Carolina Division of Marine Fisheries, 2023).
A strong outward movement of white shrimp is therefore not merely a shrimp migration. It is a moving food resource.
When those shrimp leave marsh creeks and spread toward the sound and inlet, predators that were previously separated begin encountering the same pulse of prey in increasingly narrow parts of the estuary.
The estuary briefly becomes a funnel.
The Blue Crabs Take Different Roads
Blue crabs (Callinectes sapidus) complicate the idea of a single fall migration even further because males and females do not necessarily go the same direction.
Blue crab (Callinectes sapidus) in shallow estuarine habitat; mature females eventually move toward saltier water and coastal spawning areas. | Image credit: lenora_irene, iNaturalist
Adult males generally remain farther upriver in lower-salinity water, while mature females move toward saltier portions of the estuary and eventually toward inlet and coastal spawning habitat. Females can travel considerable distances during this migration, using salinity gradients, tides, and currents to move toward the high-salinity water needed for spawning (Bell & Eggleston, 2023; Forward et al., 2003).
That split makes sense once their life cycle is considered. Females typically mate in brackish estuarine water, then store sperm until they are ready to produce an egg mass. As spawning approaches, they move toward the lower estuary and inlet, where much saltier water provides the conditions their developing larvae need. Eggs hatch near the mouth of the estuary or just beyond it, and the larvae are carried offshore before later returning toward the coast as postlarvae (Forward et al., 2003; Epifanio, 2019).
The same inlet therefore serves two directions of the blue crab life cycle: mature females move outward toward spawning water, while a later generation is carried back toward estuarine nursery habitat.
For a blue crab, the difference between a brackish river and a salty inlet is not simply scenery. One supports mating and much of adult life, while the other provides the salinity needed to begin the next generation.
A single life cycle requires both.
Rays Begin Leaving the Shallows
Large dark wings moving beneath clear water are among the more obvious signs that rays are using shallow coastal habitat during summer. By fall, where those rays appear—and how they move through the coast—begins to change.
Cownose rays (Rhinoptera bonasus) are highly mobile schooling rays that use North Carolina sounds, estuaries, and nearshore waters during the warmer months. Through summer they may be scattered across that habitat, sometimes appearing alone or in small groups over shallow flats and sounds. As fall develops, rays that have been using North Carolina estuaries begin moving toward the ocean side, while migrants arriving from farther north join the same southbound corridor along the Carolina coast.
That is when larger schools can become more noticeable along the beaches and nearshore waters. Their movement continues south toward winter habitat off Florida, with cooling water helping shape when they leave northern and estuarine habitats (Goodman et al., 2010; Omori & Fisher, 2017; Bangley et al., 2021).
Cownose rays (Rhinoptera bonasus) traveling in a school, a familiar sight as they gather and move along the coast in fall. | Image credit: Chesapeake Bay Program
For someone watching from Topsail, the rays seen scattered through the sound during summer can become part of something much larger by fall. A few dark wings moving over an estuarine flat may give way to schools traveling along the ocean side as North Carolina becomes part of the passage between northern summer waters and winter habitat farther south.
Southern stingrays (Hypanus americanus) make a quieter seasonal shift. Their summer presence along North Carolina is part of a much older warm-season pattern, with southern stingrays historically documented moving north along the Carolina coast as warmer water expands their usable habitat (Coles, 1913).
Unlike cownose rays traveling in schools higher in the water column, southern stingrays remain closely tied to the bottom. Through summer, they can be a familiar sight moving over warm sand and mud flats, along creek mouths, and through shallow estuarine water as they search the bottom for worms, bivalves, shrimp, crabs, and small fishes. Even when they move between habitats, much of that movement remains along or just above the benthic surface rather than through open water (Gilliam & Sullivan, 1993; Tilley et al., 2013).
As the shallow flats cool through fall, they become less common in the places where beachgoers may have seen them repeatedly through July and August. Their seasonal movement is not mapped nearly as clearly in North Carolina as that of cownose rays, so we cannot point to one temperature or one offshore route. What we can say is that southern stingrays are capable of moving between shallow flats and considerably deeper bottom habitat while remaining closely associated with the seafloor (Coles, 1913; Corcoran et al., 2013).
For someone watching the shallows, that change may simply look like absence. The stingray that repeatedly crossed the same warm flat all summer is suddenly harder to find—not because it has joined a large southbound school above the bottom, but because its usable benthic habitat has shifted beyond the shallows where it was easiest to see.
Red Drum Gather at the Edges
Red drum (Sciaenops ocellatus), and our state fish, add another layer to the fall movement. Young fish spend their first years closely tied to estuaries, growing quickly from roughly 12 to 14 inches by their first birthday to more than 27 inches during their second full year. They do not reach reproductive maturity quite as quickly, however. In North Carolina, most become mature around ages three to four, when they are roughly 30 to 36 inches long (Ross et al., 1995).
Red drum (Sciaenops ocellatus) grow in estuaries when young, while larger adults gather around inlets and nearshore waters during late-summer and fall spawning. | Image credit: colesutton, iNaturalist
That difference is something a beachgoer or angler can actually see. The smaller “puppy drum” encountered along marsh edges, creeks, and sounds are still growing within the estuarine part of their life cycle, while the much larger fish appearing around beaches and inlets are increasingly part of the adult population that spends more time in coastal and ocean waters. By late summer and early fall, mature red drum gather around inlets, beaches, and nearshore waters, where spawning and feeding can overlap. In North Carolina, spawning occurs from August into early October near barrier-island inlets and adjacent coastal waters. During that same period, adults move more actively between estuarine and ocean habitats (Ross et al., 1995; Bacheler et al., 2009).
That puts a large red drum outside New River Inlet directly into the same corridor carrying mullet, menhaden, shrimp, spot, croaker, and other prey toward the ocean. It may be there to spawn, to feed, or simply because its own seasonal movement has brought it into the same narrow stretch of coast.
As fall gives way to winter, mature adults increasingly move into ocean waters where temperatures remain more moderate, while younger red drum are much more likely to remain behind in the estuary (Stewart & Scharf, 2008).
The Offshore Visitors Come Close
Fall also brings some animals toward the coast before eventually carrying them away.
King mackerel (Scomberomorus cavalla) are warm-water fish that seldom move into water much below about 68°F. Through summer and the warmer part of fall, they can move surprisingly close to the beaches, inlet mouths, and nearshore reefs of North Carolina, following schools of menhaden, mullet, sardines, and other prey into places where a beachgoer or pier angler may suddenly encounter a fish that spends much of its time farther offshore (North Carolina Division of Marine Fisheries, 2022).
That window does not last. As coastal water continues cooling toward the lower edge of their preferred range, king mackerel begin shifting south and farther toward the warmer waters of the continental shelf. By winter, much of the Atlantic population has moved toward southern Florida, while some fish remain in deeper North Carolina waters near the Gulf Stream (North Carolina Division of Marine Fisheries, 2022).
For a few weeks, that creates an unusual overlap along the Onslow coast. Animals moving out of the estuary meet predators moving closer to shore to feed, while other migrants are already passing south or beginning their move offshore. An inlet or artificial reef that seemed relatively quiet several weeks earlier can suddenly sit at the crossing point of several different seasonal routes.
For a short time, it becomes an intersection.
Then the Menhaden Arrive
By October and November, another migration becomes increasingly visible.
Atlantic menhaden (Brevoortia tyrannus) move south along the Atlantic coast as fall deepens, with older and larger fish returning from summer waters farther north. Spawning can occur along the migration route from late fall into early spring, but one of the major winter gathering areas lies off North Carolina near Cape Hatteras (Lewis et al., 1987; Nicholson, 1978).
For Onslow County, that means some of the dark schools appearing beyond the breakers are part of a much larger coastwide movement passing our beaches on the way toward winter spawning waters.
Menhaden occupy an unusual place in the coastal food web. They filter tiny phytoplankton and zooplankton from the water, then gather that scattered production into dense schools of oily fish large enough for predators to chase (Lewis & Peters, 1994). Bluefish, striped bass, sharks, tunas, dolphins, and seabirds all take advantage of them, making menhaden one of the connections between plankton near the bottom of the food web and some of the largest predators along the coast (Chagaris et al., 2020; Lewis & Peters, 1994).
For a beachgoer, the first sign may simply be a dark patch offshore that does not move like a shadow. Then birds begin gathering above it. The surface breaks as predators push into the school from below, and what looked like an indistinct patch of water suddenly becomes one of the busiest places along the beach.
That is when looking up becomes as important as looking into the water.
Because another migration has arrived.
The Atlantic Flyway Meets the Fall Fish Run
The Atlantic Flyway follows the eastern edge of North America, placing the North Carolina coast directly beneath one of the continent’s major migration routes. For birds traveling hundreds or thousands of miles between breeding and wintering grounds, Onslow County is not simply coastline passing beneath their wings. Its beaches, marshes, tidal flats, sounds, and inlets can provide places to rest and replenish the energy needed for the next part of the journey (Smith et al., 2022).
The Atlantic Flyway follows the eastern edge of North America, carrying migrating birds directly along the North Carolina coast. | Image credit: Audubon
Fall makes that stop especially busy because the migration overhead is unfolding at the same time the water below is changing. Shrimp are moving out of creeks. Mullet and other fishes are funneling toward the inlets. Schools of bait gather along the beaches, and menhaden begin moving down the coast. For birds that feed on fishes and coastal invertebrates, those movements can turn the Onslow shoreline into a series of feeding opportunities along the Atlantic Flyway.
But the transition is not a clean exchange in which the summer birds simply leave and winter birds immediately take their places. It happens gradually, with departures, arrivals, and birds merely passing through overlapping for weeks.
The Birds Moving Through or South
Some of the first changes are easiest to notice in the marsh. Green herons (Butorides virescens) begin moving south from late August through October, while least bitterns (Ixobrychus exilis) also leave much of their northern breeding range for warmer winter habitat. A bird that spent summer hunting from the edge of a tidal creek may simply become harder to find as September advances (Smith et al., 2022).
Along the beaches and nesting islands, the summer community begins loosening in several directions at once. Wilson’s plovers (Anarhynchus wilsonia), least terns (Sternula antillarum), gull-billed terns (Gelochelidon nilotica), black skimmers (Rynchops niger), and sandwich terns (Thalasseus sandvicensis) begin leaving breeding areas or redistributing south along the coast. Royal terns (Thalasseus maximus) may linger longer, while ospreys (Pandion haliaetus) begin following waterways and coastlines toward wintering grounds farther south (North Carolina Wildlife Resources Commission, 2025; Smith et al., 2022).
The shorebirds make the transition even less tidy.
The eastern Willet (Tringa semipalmata semipalmata) breeds in Atlantic salt marshes, including those along the North Carolina coast, before leaving for wintering grounds that can lie as far away as northern South America. But the Willet standing on a Topsail flat in fall is not automatically one of the birds that nested here. Western Willets (Tringa semipalmata inornata), which breed in the interior of western North America, can also occur along the Atlantic coast outside the breeding season. For a few weeks, birds from very different summer landscapes may use the same Carolina shoreline (Oswald et al., 2016; Huysman et al., 2022).
Lesser yellowlegs (Tringa flavipes) and greater yellowlegs (Tringa melanoleuca) add another layer of passing traffic. They arrive from breeding grounds much farther north, with adults beginning their southward movements as early as July and younger birds following later. Along coastal North Carolina, exposed flats, shallow marsh edges, and pools of tidal water become temporary feeding grounds along that journey (Smith et al., 2022).
That makes the falling tide part of the migration too. A mudflat that looked empty beneath the previous high tide can suddenly hold Willets, yellowlegs, plovers, and other shorebirds probing exposed sediment for worms, small crustaceans, mollusks, and other prey. North Carolina barrier-island studies have found fall shorebirds shifting among the swash zone, wet sand, spits, and tidal habitat as water levels change, using different pieces of the shoreline for feeding and resting through the tidal cycle (Tarr, 2008).
For some of those birds, the stop may last days. For others, only hours. The tide falls, a feeding ground appears, and birds moving along the Atlantic coast briefly settle into it before the water—or the migration—carries them onward.
The Winter Coast Begins Arriving
The winter coast does not arrive all at once. Its first birds begin appearing in September, more follow through October, and by November the sounds, marshes, and beaches of Onslow County can hold a noticeably different community than they did at the end of summer.
On the sounds and protected water behind the barrier islands, buffleheads (Bucephala albeola) begin settling into sheltered coves, bays, and estuaries, repeatedly disappearing beneath the surface in search of small crustaceans, mollusks, and other aquatic prey. Red-breasted mergansers (Mergus serrator) arrive as well, often working shallow coastal water and estuaries in small groups as they dive after fish (Gauthier, 1993; Titman, 1999; Smith et al., 2022).
The marsh begins changing at the same time. American black ducks (Anas rubripes) appear more regularly in salt marshes, tidal creeks, ponds, and estuaries, while Green-winged teal (Anas crecca) increase in shallow protected water. Both spent the breeding season much farther north, but by fall the sounds and marshes of the Atlantic coast have become part of their winter landscape (Robinson et al., 2016; Smith et al., 2022).
Along the ocean side, the change is visible at the water’s edge. Dunlin (Calidris alpina), sanderlings (Calidris alba), red knots (Calidris canutus), and black-bellied plovers (Pluvialis squatarola) begin working beaches, shoals, exposed flats, and inlet margins. Some will remain along the southeastern coast through winter, while others are pausing only long enough to feed before continuing south. As the tide falls they spread across wet sand and exposed flats; when the water returns, they are gradually pushed toward higher beaches and roosting areas (Burger et al., 2012; Smith et al., 2022; Tarr, 2008).
Red knots make the scale of that movement especially clear. A bird standing quietly near the wrack line may have arrived from Arctic breeding grounds and may still be headed toward winter habitat in the southeastern United States, the Caribbean, or northern South America. Individual birds do not all travel the same route or distance, but for some, the Carolina coast is only one stop in a journey spanning thousands of miles (Burger et al., 2012; Smith et al., 2022).
That changes what a quiet fall beach can mean. The wet sand, tidal flats, wrack, marshes, and sheltered water are not empty spaces between destinations. For birds arriving from the north, they are places to replace the energy already spent before the next part of the migration begins.
When the Food Web Takes to the Air
Fall adds another layer of hunters above the shoreline.
Peregrine falcons (Falco peregrinus) move south along the Atlantic coast during migration, often following the same barrier islands, mudflats, and shorelines being used by migrating shorebirds. They are not interested in the mullet, shrimp, or menhaden moving below the surface. They are interested in the birds feeding around them. Shorebirds, ducks, gulls, and other coastal birds become prey themselves, adding another level to the food web moving through the coast (Smith et al., 2022).
Farther offshore, the change becomes visible in a different way. Double-crested cormorants (Nannopterum auritum) arrive along the Carolina coast in large numbers and spend much of their time diving after fish. Menhaden are among the schooling fishes they readily take, tying these winter visitors directly into the same fall movement already passing through the inlets and along the beaches (Watts et al., 2023).
Red-throated loons (Gavia stellata) and common loons (Gavia immer) begin appearing along the ocean side as well. Both spend the warmer months much farther north, but by late fall they are back in shallow marine waters, sounds, bays, and estuaries where fish are abundant. A bird that spent summer on a northern lake or tundra pond may now be diving just beyond the breakers along Topsail (Stenhouse et al., 2020; Smith et al., 2022).
Then come the northern gannets (Morus bassanus).
By late fall, they become one of the most spectacular signs that the seasonal food web has shifted. Northern gannets spend much of the nonbreeding season between New York and North Carolina, feeding almost entirely on schooling fishes such as herring, mackerel, and menhaden over the continental shelf (Mowbray, 2020; Smith et al., 2022).
From shore, a feeding aggregation can seem to appear from nowhere. Large white birds circle above a patch of ocean, fold their wings, and plunge headfirst into the water. One follows another until dozens may be dropping into the same moving patch of sea.
The important thing may not be the gannets themselves, but what they are pointing toward. Beneath them is a school of fish. Around that school may be bluefish, sharks, dolphins, or other large predators pushing the same prey toward the surface. The birds above and the predators below are using the same concentration of food from opposite directions.
What began months earlier as plankton, marsh production, and small animals feeding inside estuaries has now moved far enough through the food web to become visible from the beach as birds falling out of the sky.
What Happens if One Migration Does Not Arrive?
It is easy to think about migration as something belonging to individual species—the mullet run, the shrimp migration, the shark migration, the Atlantic Flyway. But the coast does not experience those movements separately. Predators are responding to prey, young fishes are entering estuaries when nursery habitat and food are available, adults are leaving when spawning habitat lies offshore, and blue crabs are moving between different salinity zones because different stages of their lives depend on different parts of the estuary (Warlen & Burke, 1990; Forward et al., 2003).
That means a change in one migration does not necessarily stop with the animal making it.
If fewer mullet leave an estuary, there may be less concentrated prey moving along the beach for bluefish, sharks, pelicans, and terns. The difference is not simply fewer mullet in one place. Some of the energy that spent summer accumulating inside the estuary now reaches the nearshore food web in a different amount, at a different time, or along a different route (Bacheler et al., 2005).
White shrimp show how quickly those relationships can shift. Heavy rainfall lowers estuarine salinity and can push shrimp toward the inlet earlier than they might have moved during a drier fall. Predators farther inside the estuary may encounter fewer shrimp, while those gathered nearer the inlet may suddenly encounter more. The migration still happens, but its timing changes where that pulse of food becomes available (North Carolina Division of Marine Fisheries, 2023).
Temperature can alter the overlap in another way. A coastal shark that remains farther north later into a warm fall may not encounter its prey in quite the same places or at quite the same time if those prey are responding to a different set of seasonal cues. Warmer ocean conditions are already capable of delaying southward shark migrations and extending how long some species remain in northern seasonal habitat (Manz et al., 2025).
None of this means every migration must occur on the same date each year. Coastal systems have always varied with storms, rainfall, temperature, currents, and food availability. What matters is that the movements continue to cross one another often enough for the relationships among them to persist.
A predator still has to encounter its prey. A larva still has to reach suitable nursery habitat, and a migrating bird still has to find enough food to continue south.
The timing does not have to be exact, but the meeting still has to happen.
Watching the Coast Change
By September, the first changes are already beginning. Mullet gather near the inlets, shrimp move out of tidal creeks, rays become less common over shallow flats, and feeding birds begin revealing where bait has collected near the surface.
By October and November, the same places can hold a very different community. Some animals have moved only a few miles into deeper water, while others are passing Onslow County on journeys that continue far beyond the Carolina coast.
The landscape itself looks much the same. New River Inlet still cuts through the barrier island. The marsh grass still bends with the wind. The same beach stretches north and south. What changes is who is moving through it.
For a few months each fall, Onslow County becomes a meeting place between departures, arrivals, and animals simply shifting into the next piece of habitat they need.
The landscape stays where it is. The food web moves through it.
Wilson Bay along the New River in Jacksonville, North Carolina. The landscape stays where it is, even as the food web moves through it. | Image credit: A. Mitchell
References
Allen, D. M., Govoni, J. J., Able, K. W., Buckel, J. A., Hale, E. A., Hilton, E. J., Kellison, G. T., Targett, T. E., Taylor, J. C., & Walsh, H. J. (2024). Long-term dynamics of larval and early juvenile spot (Leiostomus xanthurus) off the U.S. East Coast: Relating ocean origins, estuarine Ingress, and changing environmental conditions. Fishery Bulletin, 122(4), 162-185. https://doi.org/10.7755/fb.122.4.3
Bacheler, N. M., Paramore, L. M., Burdick, S. M., Buckel, J. A., & Hightower, J. E. (2009). Variation in movement patterns of red drum (Sciaenops ocellatus) inferred from conventional tagging and ultrasonic telemetry. Fishery Bulletin, 107(4), 405-419. https://spo.nmfs.noaa.gov/sites/default/files/pdf-content/2009/1074/bacheler.pdf
Bacheler, N. M., Wong, R. A., & Buckel, J. A. (2005). Movements and mortality rates of striped mullet in North Carolina. North American Journal of Fisheries Management, 25(1), 361-373. https://doi.org/10.1577/m04-033.1
Bangley, C. W., Edwards, M. L., Mueller, C., Fisher, R. A., Aguilar, R., Heggie, K., Richie, K., Ahr, B. J., & Ogburn, M. B. (2021). Environmental associations of cownose ray (Rhinoptera bonasus) seasonal presence along the U.S. Atlantic coast. Ecosphere, 12(9). https://doi.org/10.1002/ecs2.3743
Bell, G. W., & Eggleston, D. B. (2023). Timing and route of migration of mature female blue crabs in a large, wind-driven Estuary. Transactions of the American Fisheries Society, 152(2), 253-269. https://doi.org/10.1002/tafs.10391
Bichy, J. B. (2004). A life history assessment on the reproduction and growth of striped mullet, Mugil cephalus, in North Carolina [Unpublished master’s thesis]. North Carolina State University.
Burger, J., Niles, L. J., Porter, R. R., Dey, A. D., Koch, S., & Gordon, C. (2012). Using a shore bird (red knot) fitted with geolocators to evaluate a conceptual risk model focusing on offshore wind. Renewable Energy, 43, 370-377. https://doi.org/10.1016/j.renene.2011.11.006
Carlson, J. K., Sulikowski, J. R., & Baremore, I. E. (2006). Do differences in life history exist for blacktip sharks, Carcharhinus limbatus, from the United States south Atlantic bight and eastern Gulf of Mexico? Environmental Biology of Fishes, 77(3-4), 279-292. https://doi.org/10.1007/s10641-006-9129-x
Chagaris, D., Drew, K., Schueller, A., Cieri, M., Brito, J., & Buchheister, A. (2020). Ecological reference points for Atlantic menhaden established using an ecosystem model of intermediate complexity. Frontiers in Marine Science, 7. https://doi.org/10.3389/fmars.2020.606417
Coles, R. J. (1913). Notes on the embryos of several species of rays, with remarks on the northward summer migration of certain tropical forms observed on the coast of North Carolina. Bulletin of the American Museum of Natural History, 32, 29-35. https://www.biodiversitylibrary.org/page/26891225#page/491/mode/1up
Corcoran, M. J., Wetherbee, B. M., Shivji, M. S., Potenski, M. D., Chapman, D. D., & Harvey, G. M. (2013). Supplemental feeding for ecotourism reverses Diel activity and alters movement patterns and spatial distribution of the southern Stingray, Dasyatis americana. PLoS ONE, 8(3), e59235. https://doi.org/10.1371/journal.pone.0059235
Craig, J. K., Smith, W. E., Scharf, F. S., & Monaghan, J. P. (2015). Estuarine residency and migration of southern flounder inferred from conventional tag returns at multiple spatial scales. Marine and Coastal Fisheries, 7(1), 450-463. https://doi.org/10.1080/19425120.2015.1079578
Ellis, T. A., Buckel, J. A., Hightower, J. E., & Poland, S. J. (2017). Relating cold tolerance to winterkill for spotted seatrout at its northern latitudinal limits. Journal of Experimental Marine Biology and Ecology, 490, 42-51. https://doi.org/10.1016/j.jembe.2017.01.010
Ellis, T., Buckel, J., & Hightower, J. (2017). Winter severity influences spotted seatrout mortality in a southeast US estuarine system. Marine Ecology Progress Series, 564, 145-161. https://doi.org/10.3354/meps11985
Epifanio, C. E. (2019). Early life history of the blue crab Callinectes sapidus: A review. Journal of Shellfish Research, 38(1), 1-22. https://doi.org/10.2983/035.038.0101
Forward, R. B., Tankersley, R. A., & Welch, J. M. (2003). Selective tidal-stream transport of the blue crab Callinectes sapidus: An overview. Bulletin of Marine Science, 72(2), 347-365. https://scholars.duke.edu/publication/771475
Gauthier, G. (1993). Bufflehead (Bucephala albeola). In The Birds of North America (67th ed.). The Academy of Natural Sciences of Philadelphia & The American Ornithologists’ Union.
Goodman, M. A., Conn, P. B., & Fitzpatrick, E. (2010). Seasonal occurrence of Cownose rays (Rhinoptera bonasus) in North Carolina’s estuarine and coastal waters. Estuaries and Coasts, 34(3), 640-651. https://doi.org/10.1007/s12237-010-9355-5
Heupel, M., Carlson, J., & Simpfendorfer, C. (2007). Shark nursery areas: Concepts, definition, characterization and assumptions. Marine Ecology Progress Series, 337, 287-297. https://doi.org/10.3354/meps337287
Huysman, A. E., Cooper, N. W., Smith, J. A., Haig, S. M., Heath, S. A., Johnson, L., Olson, E., Regan, K., Wilson, J. K., & Marra, P. P. (2022). Strong migratory connectivity indicates Willets need subspecies-specific conservation strategies. Ornithological Applications, 124(3). https://doi.org/10.1093/ornithapp/duac015
Jensen, D. R., & Graves, J. E. (2020). Movements, habitat utilization, and post-release survival of cobia (Rachycentron canadum) that summer in Virginia waters assessed using pop-up satellite archival tags. Animal Biotelemetry, 8(1). https://doi.org/10.1186/s40317-020-00212-0
Krause, J. R., Hightower, J. E., Buckel, J. A., Turnure, J. T., Grothues, T. M., Manderson, J. P., Rosendale, J. E., & Pessutti, J. P. (2020). Using acoustic telemetry to estimate weakfish survival rates along the U.S. East Coast. Marine and Coastal Fisheries, 12(5), 241-257. https://doi.org/10.1002/mcf2.10095
Lewis, R. M., Ahrenholz, D. W., & Epperly, S. P. (1987). Fecundity of Atlantic menhaden, Brevoortia tyrannus. Estuaries, 10(4), 347. https://doi.org/10.2307/1351894
Lund, W. A., & Maltezos, G. C. (1970). Movements and migrations of the bluefish, Pomatomus saltatrix, tagged in waters of New York and southern New England. Transactions of the American Fisheries Society, 99(4), 719-725. https://doi.org/10.1577/1548-8659(1970)99<719:mamotb>2.0.co;2
Manz, M. H., Shipley, O. N., Cerrato, R. M., Hueter, R. E., Newton, A. L., Tyminski, J. P., Franks, B. R., Curtis, T. H., Fischer, C., Zacharias, J. P., Scott, C., Dunton, K. J., Kneebone, J., Peterson, B. J., Scannell, B. J., Dodd, J. F., & Frisk, M. G. (2025). Predictions of southern migration timing in coastal sharks under future ocean warming. Conservation Biology, 39(6), e70080. https://doi.org/10.1111/cobi.70080
McCandless, C. T., Pratt, Jr., H. L., Kohler, N. E., Merson, R. R., & Recksiek, C. W. (2007). Distribution, localized abundance, movements, and migrations of juvenile sandbar sharks tagged in Delaware Bay. In Shark nursery grounds of the Gulf of Mexico and the east coast waters of the United States (pp. 45-62). American Fisheries Society Symposium. https://doi.org/10.47886/9781888569810.ch4
Merson, R. R., & Pratt, Jr., H. L. (2001). Distribution, Movements and Growth of Young Sandbar Sharks, Carcharhinus Plumbeus, in the Nursery Grounds of Delaware Bay. Environmental Biology of Fishes, 61, 13-24. https://link.springer.com/article/10.1023/A:1011017109776
Midway, S. R., & Scharf, F. S. (2012). Histological analysis reveals larger size at maturity for southern flounder with implications for biological reference points. Marine and Coastal Fisheries, 4(1), 628-638. https://doi.org/10.1080/19425120.2012.717524
Mowbray, T. B. (2020). Northern Gannet (Morus bassanus). In Birds of the World (1.0th ed.). Cornell Lab of Ornithology. https://doi.org/10.2173/bow.norgan.01
Nicholson, W. R. (1978). Movements and population structure of Atlantic menhaden indicated by tag returns. Estuaries, 1(3), 141. https://doi.org/10.2307/1351455
Norcross, B. L., & Austin, H. M. (1988). Middle Atlantic bight meridional wind component effect on bottom water temperatures and spawning distribution of Atlantic croaker. Continental Shelf Research, 8(1), 69-88. https://doi.org/10.1016/0278-4343(88)90025-8
Omori, K. L., & Fisher, R. A. (2017). Summer and fall movement of cownose ray, Rhinoptera bonasus, along the East Coast of United States observed with pop-up satellite tags. Environmental Biology of Fishes, 100(11), 1435-1449. https://doi.org/10.1007/s10641-017-0654-6
Oswald, J. A., Harvey, M. G., Remsen, R. C., Foxworth, D. U., Cardiff, S. W., Dittmann, D. L., Megna, L. C., Carling, M. D., & Brumfield, R. T. (2016). Willet be one species or two? A genomic view of the evolutionary history of Tringa semipalmata. The Auk, 133(4), 593-614. https://doi.org/10.1642/auk-15-232.1
Packer, D. B. (1999). Essential fish habitat source document. Summer flounder, Paralichthys dentatus, life history and habitat characteristics (NOAA Technical Memorandum NMFS-NE-151). National Marine Fisheries Service. https://repository.library.noaa.gov/view/noaa/3149
Robinson, O. J., McGowan, C. P., & Devers, P. K. (2016). Updating movement estimates for American Black ducks (Anas rubripes). PeerJ, 4, e1787. https://doi.org/10.7717/peerj.1787
Roskar, G., Morley, J. W., & Buckel, J. A. (2024). Seasonality and relative abundance within an elasmobranch assemblage near a major biogeographic divide. PLOS ONE, 19(6), e0300697. https://doi.org/10.1371/journal.pone.0300697
Ross, J. L., Stevens, T. M., & Vaughan, D. S. (1995). Age, growth, mortality, and reproductive biology of red drums in North Carolina waters. Transactions of the American Fisheries Society, 124(1), 37-54. https://doi.org/10.1577/1548-8659(1995)124<0037:agmarb>2.3.co;2
Ross, S. W. (1988). Age, growth, and mortality of Atlantic croaker in North Carolina, with comments on population dynamics. Transactions of the American Fisheries Society, 117(5), 461-473. https://doi.org/10.1577/1548-8659(1988)117<0461:agamoa>2.3.co;2
Smith, M. A., Mahoney, J., Knight, E. J., Taylor, L., Seavy, N. E., Bailey, O. H., Carbone, M., DeLuca, W., Gonzalez, N. S., Jimenez, M. F., W. O’Bryan, G. M., Rao, N., Witko, C. J., Wilsey, C., & Deppe, J. L. (2022). Bird Migration Explorer. National Audubon Society. https://explorer.audubon.org/
Stenhouse, I. J., Berlin, A. M., Gilbert, A. T., Goodale, M. W., Gray, C. E., Montevecchi, W. A., Savoy, L., & Spiegel, C. S. (2020). Assessing the exposure of three diving bird species to offshore wind areas on the U.S. Atlantic outer continental shelf using satellite telemetry. Diversity and Distributions, 26(12), 1703-1714. https://doi.org/10.1111/ddi.13168
Stewart, C. B., & Scharf, F. S. (2008). Estuarine recruitment, growth, and first‐year survival of juvenile red drum in North Carolina. Transactions of the American Fisheries Society, 137(4), 1089-1103. https://doi.org/10.1577/t07-176.1
Sutherland, D. F., & Fable, Jr., W. A. (1980). Results of a king mackerel (Scomberomorus cavalla) and Atlantic Spanish mackerel (Scomberomorus maculatus) migration study, 1975–79 (NOAA Technical Memorandum NMFS-SEFC-12). National Marine Fisheries Service. https://repository.library.noaa.gov/view/noaa/5385
Tilley, A., López-Angarita, J., & Turner, J. (2013). Effects of scale and habitat distribution on the movement of the southern stingray Dasyatis americana on a Caribbean atoll. Marine Ecology Progress Series, 482, 169-179. https://doi.org/10.3354/meps10285
Titman, R. D. (n.d.). Red-breasted Merganser (Mergus serrator). In The Birds of North America (443rd ed.). A. Poole & F. Gill.
Warlen, S. M., & Burke, J. S. (1990). Immigration of larvae of fall/Winter spawning marine fishes into a North Carolina Estuary. Estuaries, 13(4), 453. https://doi.org/10.2307/1351789
Warlen, S. M., & Chester, A. J. (1985). Warlen, S. M., & Chester, A. J. (1985). Age, growth, and distribution of larval spot, Leiostomus xanthurus, off North Carolina. Fishery Bulletin, 83(4), 587–599. Fishery Bulletin, 83(4), 587-599. https://spo.nmfs.noaa.gov/sites/default/files/pdf-content/fish-bull/warlen.pdf
Watts, B. D., Paxton, B. J., Hines, C., & Anderson, S. K. (2023). Estimating potential menhaden consumption by double-crested cormorants along the coast of North Carolina. Frontiers in Marine Science, 10, 1193429. https://doi.org/10.3389/fmars.2023.1193429
White, M. L., & Chittenden, Jr., M. E. (1977). Age determination, reproduction, and population dynamics of the Atlantic croaker, Micropogonias undulatus. Fishery Bulletin, 75(1), 109-123.
Somewhere between watching my daughter catch waves and standing in the surf zone waiting for the next decent one to come through, I noticed the fish.
They were small—anchovy-like from where I stood, although the glare on the water and the constant movement made identification nearly impossible. What caught my attention wasn’t what they were. It was the fish on the move beside us, all traveling in the same narrow line for almost four hours.
They were moving parallel to the beach in a line perhaps four inches wide, almost exactly where the waves were breaking.
A wave would come through hard enough to knock us backward. Water rushed toward shore and then pulled against our legs as it returned. My daughter and I moved with it.
The fish didn’t seem to.
The line continued.
A little farther offshore was another line of larger fish. They were less tightly packed, but moving along the same general stretch of coast. Beyond them, one or two long, slender fish held near my daughter’s board. We couldn’t identify them with certainty, although their shape was consistent with one of our larger needlefishes, possibly a houndfish. They didn’t appear to be simply passing through. They would dart toward the smaller fish, take one, and return.
Farther still, just beyond the breakers, something much larger came partly out of the water while apparently feeding. It happened too quickly to tell whether it was a shark, large fish, or something else.
Then the line of little fishes passing in front of me suddenly broke.
Fish scattered and began leaping from the water, fleeing something I couldn’t see. Almost immediately, there seemed to be another pursuit underway.
That seemed like a good time for us to take a short break on the beach.
We had been in the water for nearly four hours by then, and those little fish had been passing us for much of it.
It was only after watching them for so long that the strange part became obvious.
The water looked like one place. We had been watching fish on the move through the surf zone all afternoon.
The fish were behaving as though it wasn’t.
The Line That Didn’t End
Standing in the surf, it is easy to think of the shallow water as a temporary place.
Waves arrive. Water runs up the beach and retreats. Sand shifts beneath your feet. A few yards offshore, another wave rises over a bar and breaks. Everything seems to be moving too much for anything resembling a pathway to exist.
To a fish, however, that same water contains structure.
Even water only a few inches or a foot deep can hold its own patterns. Small runnels form behind sandbars, wave energy changes as water crosses them, and fishes can move parallel to shore through these shallow strips rather than spreading evenly across the surf. The exact species may change from beach to beach, but the pattern is not unusual: fishes sort themselves through very small differences in shallow-water habitat (Layman, 2000).
Look closely and the tiny fish begin to appear—a narrow line moving through water that, at first glance, looks almost empty. | Image credit: A. Mitchell
Late summer can make those patterns especially noticeable. Along our part of the coast, both the number of fish and the variety of species using the surf climb through the warm months, reaching their highest levels from June through August (North Carolina Sea Grant, 2019).
So the little fish moving past our legs weren’t occupying empty water between the beach and the ocean.
They were inside habitat. And habitat has shape.
Mapping the Invisible Structure
Most of that shape disappears when we look across the water from shore.
We can see the obvious pieces. Waves often reveal where a sandbar rises toward the surface. Darker water may hint at a trough. A break in the waves can sometimes betray a deeper channel. Farther out, the water deepens into another shade.
For a small fish, those changes don’t have to be dramatic to matter.
A few inches of depth can change how quickly the water moves, how much wave energy reaches a spot, what food passes through and which animals can follow. Temperature and wave conditions add another layer. Together, they turn what looks like one open stretch of surf into a collection of much smaller usable spaces (Olds et al., 2018).
The difference between standing here and standing three feet farther out may barely register to us.
To a fish only a few inches long, it can mean different water.
That becomes easier to picture when we pull back and look at the coast beneath us.
Off Onslow County, the continental shelf doesn’t plunge quickly into deep water. It stretches gradually away from shore across a broad, shallow part of Onslow Bay. Near the beach, the bottom is mostly sand, with shell fragments and coarser material mixed through some areas. Closer to shore, that otherwise gentle slope is interrupted again and again by the smaller features we actually feel beneath our feet—bars, dips, troughs and runnels that waves and currents continually reshape (North Carolina Coastal Resources Commission Science Panel, 2026; Tyler & Kowalewski, 2018).
Along the Onslow County coast, the shallow sandy bottom rises and falls in subtle bars, troughs, and runnels that can shape how fish use the surf zone. | Image credit: A. Mitchell
To us, one of those dips may simply feel like the water suddenly came a little higher on our bodies.
For a fish only a few inches tall, it can be a different piece of the landscape.
That doesn’t mean the little school we watched was tracing a particular underwater trough. We couldn’t see the bottom well enough to know that.
But their persistence was revealing something.
Waves repeatedly pushed us out of position while fish continued moving through approximately the same narrow part of the surf. Whatever they were responding to—depth, current, food, protection, or some combination—the fish could perceive differences in that water that we couldn’t.
Their movement made some of the invisible structure visible.
Why the Smallest Fish Remain Close to Shore
There is something counterintuitive about watching tiny fish choose the place where waves are breaking. It doesn’t look protected.
For us, it was the part of the water most likely to knock us over.
But safety underwater doesn’t necessarily look like calm water.
For a small fish, extremely shallow water can make life more difficult for some of the animals trying to catch it. A larger predator may still enter—and plenty do—but depth, turbulence and room to maneuver change as the water shoals toward the beach. Juvenile fishes can shift into different depths as they balance the food available there against the risk of being eaten, so sometimes moving only a little shallower can change the odds (Layman, 2000; Miltner et al., 1995; Munsch et al., 2016).
The breaking surf may look rough and exposed to us, but for small fish, shallow water can change both access to food and the odds of being caught by a larger predator. | Image credit: A. Mitchell
And there is plenty to eat.
During summer, some of the smallest schooling fishes—including bay anchovies, striped anchovies and Atlantic silversides—feed largely on plankton carried through the surf. Summer zooplankton can include copepods, mysids, crab larvae and other tiny animals whose numbers shift with tides and time of day (DeLancey, 1987, 1989). Other fishes take food from the sand itself, including mole crabs, passing energy from animals buried beneath the beach into fishes farther up the food web. Surveys of southeastern surf zones have found dozens of species of fish and swimming invertebrates moving through these waters over the seasons (Anderson et al., 1977).
Even some of the food at the very bottom of that web is being produced right there. The phytoplankton growing in southeastern North Carolina’s surf can make these shallow waters considerably more productive than the coastal ocean just offshore, although not as productive as our estuaries (Cahoon et al., 2017).
There is something else happening in all that breaking white water too.
Warm water cannot hold as much oxygen as cooler water. But every time a wave breaks, it churns air into the water. On a hot August day, the same foam and bubbles tossing us around are also helping oxygen move between the air and the shallows (Deike, 2022).
That doesn’t mean the fish were following an oxygen-rich pathway. We couldn’t know that from what we saw. It is simply another reminder that the breaking surf is not just rougher water. Physically and chemically, things are happening there that are different from the calmer water only a short distance away.
The water washing around our ankles is therefore not simply the edge of somewhere more biologically important. It produces food, carries food, exchanges gases with the air—and fishes use it.
That makes the shallow surf something more complicated than a hiding place. A young fish may be balancing several things at once: finding enough food, spending as little energy as possible to get it, and remaining somewhere its chances of becoming food are lower. Different species solve that problem differently.
Juvenile Florida pompano and gulf kingfish offer a good example. Rather than constantly traveling along the coastline, some can remain surprisingly attached to particular stretches of surf-zone nursery habitat for weeks (Ross & Lancaster, 2002).
So even a fish that appears to be traveling may still be working within a familiar piece of shoreline—feeding through it, shifting with the tide, or repeatedly using the same shallow habitat.
The scale of movement matters as much as the movement itself.
The Edge Is Where Dinner Waits
Where prey gather predictably, predators gain an advantage too.
That made the behavior we saw especially interesting. Houndfish, one possible match for those long fish, are large needlefishes built to take other fish, and the ones near us seemed less interested in charging through the entire school than in picking off individuals. They waited, darted toward the passing fish, took one, then returned to approximately the same area. Meanwhile, the line of small fishes carried on like nothing had occurred.
Farther out, where the water had changed to deep green, something much larger appeared to be doing its own version of the same thing. Whatever the animal was, we saw it break the surface more than once in approximately the same area while fish were there.
A predator doesn’t have to search every yard of open water equally.
Sometimes the predator is little more than a glimpse. A small fin breaking the surface (upper right of image) can be the only visible clue that something larger is working the same patch of water as the baitfish. | Image credit: A. Mitchell
Schooling fishes gather where conditions favor them, and those concentrations can be shaped by depth, temperature, currents and other physical features. When prey collect in one place instead of being scattered widely, feeding opportunities become concentrated there too (Goetsch et al., 2023; Olds et al., 2018).
Surf fishermen have been reading that relationship from above the water for generations. A trough, a cut through a sandbar or a sudden concentration of bait can be a clue not only to where the smaller fish are gathering, but to where something larger may come looking for them (Ward, n.d.).
What looked from our perspective like separate layers of fish may therefore have been something more dynamic.
The smallest fish were using conditions that suited them. Their concentration, in turn, created an opportunity for a predator capable of working alongside that concentration. What gave one animal access to plankton or a little more protection could simultaneously make it easier for another animal to find dinner.
The fish may disappear beneath the surface, but the water can still give it away—a brief wake or disturbance marking movement that is otherwise hidden from view. | Image credit: A. Mitchell
It wasn’t simply a food chain conveniently lined up from smallest fish near shore to largest predator offshore. Each animal was using the same physical landscape differently, and one animal’s useful habitat could become another animal’s hunting ground.
The structure beneath the water wasn’t just organizing where fish could move.
It was helping organize where encounters between them could happen.
When the Line Breaks
The fish themselves add another layer.
Once individuals gather into a school, they begin responding not only to the water and predators around them, but to one another.
“Safety in numbers” captures only part of what that accomplishes. A fish in a school has neighbors watching in many directions, and information about danger can move rapidly through the group. Individuals continually adjust their spacing and direction in response to nearby fish, habitat and perceived threats, so a school can tighten, turn or reorganize without every fish having to detect the predator independently (Munsch et al., 2016).
There are tradeoffs. A large school may be easier to notice than a lone fish, and crowding means sharing food and space. But once a predator attacks, the group can make choosing and isolating a single target much harder. Instead of one fish moving through open water, the predator encounters many similar bodies changing direction almost at once.
And all of that coordination has to happen while the water beneath them is moving too.
A school in the shallow surf isn’t reacting to a predator against a blank background. Depth is changing. Waves are passing through. Currents are pushing alongshore and back toward the sea. The fish have to stay together while continuously adjusting to the landscape around them.
Then an attack can rearrange everything in seconds.
A school may compress, turn sharply, split apart, or scatter as the threat moves through it. Sometimes the quickest route away is upward, and baitfish begin breaking the surface.
Sometimes the chase shows itself before the predator does. A small patch of agitated water can be the only sign that the school beneath the surface has suddenly changed direction. | Image credit: A. Mitchell
From above, that sudden spray of little bodies can look almost disconnected from what caused it. The predator may never become visible at all. What we see is the response moving through the school—the orderly shape breaking apart and reforming as hundreds of tiny decisions happen at once.
The line, in other words, was never simply a line.
It was a coordinated group whose shape could change almost instantly when the balance between traveling, feeding and surviving changed.
Just Beyond the Breakers
The surf zone doesn’t end at a precise biological boundary where the last wave breaks.
The water on either side of that breaker is connected, but the conditions are changing. Depth increases. The bottom falls farther away. Wave energy changes. Animals that can move comfortably through one part of that gradient may use another part differently, and fishes can cross between them as their needs change (Olds et al., 2018).
Beyond the shallow surf, the water deepens and the habitat changes with it—but the boundary is not a hard line. Fish move back and forth across that transition as their needs change. | Image credit: A. Mitchell
That makes the surf less like a row of separate habitats and more like a transition.
On the landward side are the shallow runnels and troughs used by small fishes. Farther out, those waters connect with the open nearshore ocean. Along the beach, the same surf runs toward inlets, and beyond those inlets lie estuaries and nursery habitats. For a fish, these aren’t necessarily separate places encountered one at a time. They can be connected parts of its life.
That connection becomes particularly important for young fishes.
Some species arrive in shallow coastal waters during early life stages. Others move between estuarine nurseries and the ocean as they grow. Still others use the surf primarily to feed or travel. The importance of any one patch of shallow water therefore depends partly on what it connects to (Olds et al., 2018; Ross & Lancaster, 2002).
Predators cross those connections as well. As prey move into deeper water, toward an inlet or along the shoreline, they become available to a different mix of animals. Conversely, a predator following prey does not need to remain on one side of a line humans call “the breakers.”
The larger animal we glimpsed offshore isn’t evidence of a particular cross-shore food chain. We don’t know what it was, what it caught, or why it was feeding there.
What its presence does illustrate is that the ecological landscape continues beyond what we can easily see from knee- or waist-deep water.
The surf is an edge, but it is also a bridge.
Movement Within Movement
Follow that bridge along the North Carolina coast and the scale changes again.
Our long stretches of open beach are repeatedly interrupted by inlets, and behind those inlets lie sounds, tidal creeks, marshes and estuaries. To us, those places often have separate names and boundaries. To a fish moving through them, they are connected pieces of habitat used at different times and for different reasons.
The surf itself can be both a place to feed and a route between those places (Olds et al., 2018). A juvenile using shallow water may later move deeper, follow the coast toward an inlet, or leave a nursery area as it grows. Another fish may do almost the opposite and remain surprisingly local. Juvenile Florida pompano and gulf kingfish tagged along southeastern North Carolina beaches, for example, could remain faithful to relatively small areas of surf for extended periods (Ross & Lancaster, 2002).
A few feet with the tide, weeks along one beach, a journey between estuary and ocean, or a seasonal movement along hundreds of miles of coastline can therefore all belong to the same animal at different times in its life.
What looks like one continuous stretch of water can connect very different habitats—from the shallow surf to inlets, estuaries, and the nearshore ocean. | Image credit: A. Mitchell
Those aren’t separate stories.
They fit inside one another.
That is what makes a shallow stretch of surf important even when it is not a final destination. It may be feeding ground, nursery habitat, temporary refuge, travel corridor—or simply the connective piece that allows a fish to reach the next habitat it needs.
The coastline is not only habitat made of places.
It is habitat made of connections between them.
The Late-Summer Coast
By August, many of those connections are busy.
The surf fills with its greatest abundance and variety of fishes during the warm months from June through August (North Carolina Sea Grant, 2019). The shallowest surf holds its greatest abundance and diversity during this part of the year (Layman, 2000).
For someone walking into warm August water, that means the crowd beneath the surface can be very different from the one occupying the same beach in winter.
By late summer, the shallow surf can look almost unchanged from day to day while the mix of fish moving through it shifts with temperature, tide, food, and life stage. | Image credit: A. Mitchell
Some of the year’s young fishes have had months to grow. Seasonal changes in plankton and animals living on and beneath the sand alter the food available to them, while water temperature, tides, waves and each species’ own life cycle influence which fishes are present and where they spend their time (Anderson et al., 1977; DeLancey, 1987, 1989; Olds et al., 2018; Wickliffe et al., 2019).
Those changes ripple upward. Small fishes link plankton and other tiny prey with larger predatory fishes, and dense gatherings of forage fish can create concentrated feeding opportunities for predators higher in the food web (Goetsch et al., 2023).
But even “late summer” doesn’t describe one fixed community.
The tide can rearrange the shallow habitat over the course of hours. More species enter the very shallow surf at high tide than at low tide, and the community changes again after dark as adult predators move into water they use differently during the day (Layman, 2000).
Temperature, tide, light and life stage change it.
All of those cycles overlap along a coastline where animals are also arriving, leaving, feeding, growing and moving between habitats.
The shoreline may stay in the same place on our map.
Ecologically, it is never quite the same place twice.
Looking at the Water Differently
What began as an odd little line of fish turned out to be a glimpse of several things happening at once.
The shallow surf had physical structure even where we couldn’t clearly see it. That structure could change where food collected, where small fishes found useful habitat, and where predators encountered prey. The schools themselves added another layer, responding not only to the water around them but to one another. Beyond them, the surf connected outward toward deeper water and alongshore toward inlets, estuaries and larger movements taking place along the coast.
None of that requires every fish we saw to have been following a migration route.
In some ways, that makes the afternoon more interesting.
Movement in the ocean doesn’t begin with the thousand-mile journey of a shark or a sea turtle. It can begin with an animal responding to a few inches of depth, a shifting tide, a patch of food or the sudden arrival of a predator. Those small decisions accumulate across schools, habitats, seasons and coastlines until they become some of the larger patterns we recognize.
None of those animals needed the boundaries to be visible to us.
The fish were already responding to depth, water movement, food, risk, season and one another. Their paths crossed a landscape hidden beneath waves and glare.
Maybe that is one of the easiest things to miss when we stand at the edge of the ocean.
We look out and see water.
Sometimes, if we stay there long enough, the animals begin drawing the map.
Once you know what to look for, the water stops looking empty. Larger fish move through the same surf that, from a distance, can seem almost featureless. | Image credit: A. Mitchell
References
Allen, L. G., & Pondella II, D. J. (2006). Surf zone, coastal pelagic zone and harbors. In The Ecology of Marine Fishes: California and Adjacent Waters (pp. 149-166). University of California Press.
Cahoon, L. B., Bugica, K., Wooster, M. K., & Dickens, A. K. (2017). Factors affecting surf zone phytoplankton production in southeastern North Carolina, USA. Estuarine, Coastal and Shelf Science, 196, 269-275. https://doi.org/10.1016/j.ecss.2017.07.012
Deike, L. (2022). Mass transfer at the ocean–atmosphere interface: The role of wave breaking, droplets, and bubbles. Annual Review of Fluid Mechanics, 54(1), 191-224. https://doi.org/10.1146/annurev-fluid-030121-014132
DeLancey, L. B. (1989). Trophic relationship in the surf zone during the summer at Folly Beach, South Carolina. Journal of Coastal Research, 5(3). https://journals.flvc.org/jcr/article/view/78162
Goetsch, C., Gulka, J., Friedland, K., Winship, A., Clerc, J., Gilbert, A., Goyert, H., Stenhouse, I., Williams, K., Willmott, J., Rekdahl, M., Rosenbaum, H., & Adams, E. (2023). Surface and subsurface oceanographic features drive forage fish distributions and aggregations: Implications for prey availability to top predators in the US Northeast shelf ecosystem. Ecology and Evolution, 13(7), e10226. https://doi.org/10.22541/au.167163077.72855489/v1
Koval, G. N., Dugan, J. E., & Hamilton, S. L. (2025). Seasonal variation and response of surf zone fish assemblages to environmental variables in the Northeast Pacific. Continental Shelf Research, 293, 105526. https://doi.org/10.1016/j.csr.2025.105526
Layman, C. (2000). Fish assemblage structure of the shallow ocean surf-zone on the Eastern Shore of Virginia barrier islands. Estuarine, Coastal and Shelf Science, 51(2), 201-213. https://doi.org/10.1006/ecss.2000.0636
Miltner, R. J., Ross, S. W., & Posey, M. H. (1995). Influence of food and predation on the depth distribution of juvenile spot (Leiostomus xanthurus) in tidal nurseries. Canadian Journal of Fisheries and Aquatic Sciences, 52(5), 971-982. https://doi.org/10.1139/f95-096
Munsch, S., Cordell, J., & Toft, J. (2016). Fine-scale habitat use and behavior of a nearshore fish community: Nursery functions, predation avoidance, and spatiotemporal habitat partitioning. Marine Ecology Progress Series, 557, 1-15. https://doi.org/10.3354/meps11862
Olds, A. D., Vargas‐Fonseca, E., Connolly, R. M., Gilby, B. L., Huijbers, C. M., Hyndes, G. A., Layman, C. A., Whitfield, A. K., & Schlacher, T. A. (2017). The ecology of fish in the surf zones of ocean beaches: A global review. Fish and Fisheries, 19(1), 78-89. https://doi.org/10.1111/faf.12237
Parker, R., & Ross, S. W. (1986). Observing reef fishes from submersibles off North Carolina. Northeast Gulf Science, 8(1). https://doi.org/10.18785/negs.0801.03
Ross, S. W., & Lancaster, J. E. (2002). Movements and site fidelity of two juvenile fish species using surf zone nursery habitats along the southeastern North Carolina coast. Environmental Biology of Fishes, 63(2), 161-172. https://doi.org/10.1023/a:1014287917297
Tyler, C. L., & Kowalewski, M. (2018). Regional surveys of macrobenthic shelf invertebrate communities in Onslow Bay, North Carolina, U.S.A. Scientific Data, 5(1). https://doi.org/10.1038/sdata.2018.54
Ulanski, S. (2011). Fishing North Carolina’s Outer Banks: The complete guide to catching more fish from surf, pier, sound, and ocean. University of North Carolina Press.
Wilber, D., Clarke, D., Ray, G., & Burlas, M. (2003). Response of surf zone fish to beach nourishment operations on the northern coast of New Jersey, USA. Marine Ecology Progress Series, 250, 231-246. https://doi.org/10.3354/meps250231
At low tide, an oyster reef can look like the remains of something rather than the beginning of it.
Gray shells rise unevenly from the mud. Some are tightly closed, their animals hidden inside. Others have been opened by predators, weakened by sponges, broken by waves, or left behind by oysters that died years before. Barnacles spread across their ridges. Mud crabs retreat into the narrow spaces between them. Small fish hold near the edges until the falling water carries them toward deeper channels.
Nothing about the reef appears to be moving.
Yet movement is what brought every oyster there.
The eastern oyster, Crassostrea virginica, begins life drifting through the water, small enough to travel wherever tides, winds, and currents carry it. For its first few weeks, it has no permanent place in the sound and no guarantee that it will ever find one.
Then, if it survives long enough, it must stop.
Once an oyster attaches, it will remain in that exact place through changing tides, heavy rain, summer heat, predators, disease, sediment, harvest, and whatever else the sound sends across its gills.
It cannot search for better water.
It cannot climb away from the mud.
It cannot leave when the season changes.
Its life depends upon finding the right place once—and upon what earlier oysters left there before it arrived.
Before the Oyster Has a Shell We Recognize
During the warmer months, adult oysters release eggs and sperm directly into the surrounding water. Fertilization takes place outside the shell, producing microscopic embryos that soon become part of the plankton.
They do not yet resemble the oysters exposed along a low-tide reef.
They are small, mobile, and carried almost entirely by the water around them.
Eastern oyster life cycle, from spawning and free-swimming larvae to settlement,, spat, and adulthood. | Image credit: NOAA Fisheries
Over the next two to three weeks, the larvae pass through several stages while tides move them through the estuary. A larva may be carried from a reef into a creek, pushed toward a marsh edge by wind, or swept farther downriver as freshwater moves through the system. Some remain close to the place where they were spawned. Others may settle in another part of the sound entirely (Hillman & Galtsoff, 1965; Kennedy, 1996).
Most never reach that point.
They are eaten by other plankton-feeding animals. They arrive in water they cannot tolerate. They sink onto soft mud where no hard surface remains exposed. They may reach the bottom only to be buried before they can attach.
An adult female may release millions of eggs during a spawning season (Kennedy, 1996).
That number does not describe how easily oysters survive.
It reveals how many beginnings the estuary loses.
Near the end of its drifting life, the larva develops a temporary foot and begins testing the surfaces below it. It is searching for something firm enough to hold it above the mud.
Stone, concrete, marl or limestone may work. But old oyster shell offers something more familiar: a hard surface already shaped by the reef and positioned where another oyster once managed to survive (Theuerkauf et al., 2015).
When the larva finds that surface, it cements itself permanently in place. Its drifting life ends, and it becomes a juvenile oyster called spat.
This arrival of a new generation is called recruitment (Kennedy, 1996).
But spawning alone does not create recruitment. Larvae must survive the water, find a surface, attach, and remain alive after settlement.
The difference between a river filled with oyster larvae and a river rebuilding an oyster reef lies in what those larvae find when they are finally ready to stop.
The Place Where It Stops
Once attached, the young oyster becomes part of a world that moves around an animal that cannot.
Water enters between its two valves and passes across the gills. Microscopic cilia guide suspended particles toward the mouth, where the oyster sorts what has arrived. Some particles become food. Others are bound in mucus and rejected.
Eastern oysters feed largely on phytoplankton—microscopic algae suspended within the water—although they may also consume bacteria, protozoans, organic material, and other particles small enough to use (Hillman & Galtsoff, 1965; Kennedy et al., 1996).
This is the process we describe when we say an oyster filters water.
The oyster is not cleaning the sound as a separate service.
It is trying to eat.
The oyster therefore lives within a constant exchange between opportunity and risk. The same tide that carries food may bring saltier water, predators, larvae, sediment, or disease. Rainfall may lower salinity enough to offer relief from some marine organisms while forcing the oyster to remain closed. Warmer water may support rapid growth while increasing the demands placed upon the animal.
Oyster reefs create habitat and influence water quality, but the oysters within them remain exposed to changing salinity, temperature, oxygen, sediment, disease, and predators. | Image credit: Estuary Chesapeake
None of those conditions remains fixed.
New River does not carry the same water after several dry weeks that it carries after days of heavy rain. Stump Sound does not behave the same near an inlet as it does within a quieter creek. Wind may hold water against one shoreline, while the tide pulls it away from another.
A few feet of elevation within the reef can matter as well.
An oyster growing near the upper surface receives more moving water and remains farther above accumulating sediment. Another only inches lower may be repeatedly coated with mud.
To us, both oysters appear to occupy the same reef. To the oysters, they may inhabit very different places (Kinsella, 2019; Kennedy et al., 1996).
Growing Where It Landed
A newly settled oyster begins with a thin shell and almost no control over what happens next.
Mud crabs can crush it. Small predators can peel it from the surface. Barnacles, mussels, tunicates, algae, and neighboring oysters compete for the same exposed space. A layer of sediment thin enough to overlook from above may bury an oyster that has only recently become visible (Theuerkauf et al., 2015).
If it survives, its shell begins to thicken.
The oyster does not grow into the smooth, symmetrical form we might expect from something sold on ice. Wild oysters take the shape their surroundings allow. They grow around one another, into narrow openings, across old shell, and toward whatever space remains exposed to the water (Theuerkauf et al., 2015).
Those ridges and uneven curves are not mistakes. They are the record of a life lived without moving.
As neighboring oysters grow together, their shells begin to lock into a larger structure. Spaces open among them. Mud crabs disappear into the crevices. Blennies, gobies, worms, shrimp, barnacles, and anemones occupy surfaces the oysters created simply by surviving in the same place (Theuerkauf et al., 2015).
The reef is not built according to a plan. It emerges from generation after generation solving the same problem together: stay above the mud, remain exposed to moving water, and leave another hard surface behind.
In North Carolina, an oyster may reach the legal market size of three inches in approximately two to three years, although the actual rate varies greatly among locations and between wild and cultivated oysters (North Carolina Division of Marine Fisheries, 2022).
A farmed oyster may be raised above the bottom, protected within bags or cages, cleaned of fouling organisms, and tumbled to create a deeper, more uniform shell. A wild oyster receives no such adjustment. It grows wherever its larval journey ended. That difference helps shape the shell, but the water still shapes both (Kinsella, 2019).
Neither escapes the sound.
When an Oyster Becomes Part of a Place
An oyster growing in New River is the same species as one growing elsewhere along the Atlantic Coast.
But place leaves a mark.
The water moving through the river, the sediment beneath the reef, the distance from the inlet, and the crowded shells around it all influence how an oyster grows. Over time, those conditions can produce oysters recognized not only by species, but by where they came from.
By the beginning of the twentieth century, people were speaking of the New River oyster as something distinctive.
At a fisheries convention held in New Bern in 1911, speakers described New River oysters as unusually large and desirable. The largest were called “whoppers,” and one account placed them among the finest oysters produced along the Atlantic Coast (North Carolina Geological and Economic Survey, 1911).
Tonging for oysters circa 1900, in presumably, Pamlico Sound. | Image credit: C. Graves
The description carried some salesmanship. The convention was intended partly to persuade state leaders that North Carolina’s fisheries needed attention and reform. Still, the language reveals something important.
People believed New River produced an oyster worth naming.
The largest were being packed and shipped to markets in Washington, Baltimore, Philadelphia, and New York. Meanwhile, oysters sold closer to the river were sometimes mixed with smaller harvests brought from Myrtle Grove and Stump sounds (North Carolina Geological and Economic Survey, 1911).
The oysters that had come to represent New River were leaving it, and their size made that loss more important than it first appeared.
Oyster dredging on Pamlico Sound ca. 1900. | Image credit: C. Graves
Eastern oysters do not always remain permanently male or female. Many begin reproductive life as males and later function as females, although individuals may change more than once. Size, age, energy reserves, and surrounding conditions all influence that development (Kennedy, 1996).
Larger females can produce far more eggs than smaller oysters. Older oysters have also survived enough seasons to reproduce repeatedly, add height to the reef, and build shells larger than those they inherited (Kennedy, 1996).
Every whopper removed from New River was therefore more than a large meal.
It was a potential parent, part of the reef’s living height, and one more shell that might eventually have given another oyster somewhere to stop (Kinsella, 2019).
The Reefs People Returned To
The New River oyster had acquired a modern name, but the relationship between people and these reefs was already ancient.
Archaeological sites along the coast preserve part of that relationship. Some contain shell middens—places where oyster and clam shells accumulated alongside fish bones, tools, ceramics, charcoal, hearth remains, and other traces of daily life. A midden may appear at first to be little more than a pile of discarded shell (Claassen-MacClelland, 1979).
Oyster shells accumulated in middens record repeated harvest, meals, and generations of people returning to the same estuarine resources. | Image credit: Library of Congress
It is also evidence of repeated return.
People harvested oysters from particular waters, carried them away from the reef, prepared them near homes or gathering places, and left the shells behind. Layer upon layer, those remains show that shellfish were not an occasional food gathered at the edge of an otherwise land-based life. They were part of how people lived beside the estuary.
The shells may also preserve clues about the waters in which the oysters grew. Their size, shape, growth, chemistry, and attached organisms can reflect earlier environmental conditions (Mouchi et al., 2025).
But a midden is not a direct picture of an ancient reef. People selected the oysters they wanted, harvested some places more often than others, and transported shell away from the water. Erosion, development, soil chemistry, and the uneven reach of archaeological surveys further shaped what remained available to find (Claassen-MacClelland, 1979).
The record cannot tell us exactly how many oysters lived in New River at any one time. It tells us that oysters were abundant enough, reliable enough, and important enough for people to return to them across generations.
By the late nineteenth century, those familiar oyster grounds were also becoming mapped resources.
During the 1880s, Lieutenant Francis Winslow’s surveys began translating North Carolina’s naturally productive oyster bottom into measured boundaries, distinguishing public oyster rocks from areas that might be opened to private cultivation (North Carolina Geological Survey, 1887).
Winslow’s “Map of Pamplico Sound and Tributaries” | Image credit: Outer Banks History Center
Winslow’s most extensive work focused on the large sounds of northeastern North Carolina, but the surveys reflected a broader change along the coast. Reefs known through experience and repeated use were being placed within lines that could determine where oysters were harvested, cultivated, leased, or protected.
Decades later, federal surveyors mapped oyster reefs in New River for another reason.
In 1933, the U.S. Coast and Geodetic Survey charted the river and its tributaries from the inlet toward Jacksonville. Its surveyors recorded channels, shoreline features, depths, and anything a vessel might encounter.
Some oyster reefs rose high enough to matter.
A 1933 chart of New River showing oyster rocks — reefs exposed or awash at low tide — recorded as part of the navigable landscape. | Image credit: Nautical Charts Online
Features shown with the symbol commonly used for rocks awash were identified in the survey records as oyster rocks exposed or washed over at normal low water (U.S. Coast and Geodetic Survey, 1933).
These were not isolated shells scattered across the bottom. They were reefs substantial enough to interrupt navigation and become part of the charted river.
The charts cannot tell us how many living oysters occupied each reef, whether the reefs were still growing, or how much had already been lost to harvest and shell removal. They show what remained visible enough to measure.
At low tide, generations of oysters became geography.
Intertidal oyster rocks exposed at low tide, where generations of living and dead shell build the reef upward from the soft bottom. | Image credit: CoastalReview.org
What Was Taken With the Oyster
The living oysters were not the only useful part of the reef.
Their shells could be burned into lime, spread onto agricultural land, crushed into roads, or used in construction. Once carried away from the sound, however, those shells could no longer become part of another oyster generation (Carter et al., 2006).
The reef was harvested twice.
First came the oyster.
Then came the place where its descendants might have settled.
This was the deeper loss behind the warnings raised at the 1911 fisheries convention. Participants were not only concerned that large New River oysters were disappearing from local markets. They also discussed the importance of leaving or returning shell to the water.
One proposal called for shell to be replaced according to the number of oysters removed (North Carolina Geological and Economic Survey, 1911).
The larva explains why.
A high reef keeps much of its shell exposed above the soft bottom. Water moves through the spaces between oysters. Young spat settle onto hard surfaces rather than disappearing into mud. Crabs and fish occupy openings that persist even after the animals that formed them die (North Carolina Division of Marine Fisheries, 2022; Theuerkauf et al., 2015).
Fewer oysters leave less shell. Less shell gives fewer larvae somewhere to stop (North Carolina Division of Marine Fisheries, 2022; Theuerkauf et al., 2015).
The reef does not simply lose its occupants. It loses the architecture required to replace them.
Returning What the Larva Needed
By 1911, fisheries representatives were warning that New River’s celebrated oysters were disappearing and that the shell removed with them needed to be returned to the water. Four years later, North Carolina began formally planting cultch onto oyster grounds (Daniel, 2015; North Carolina Geological and Economic Survey, 1911).
The reasoning was simple. Oyster larvae could still drift through the estuary, but without exposed hard surface, many had nowhere to settle.
At first, the material returned was largely oyster shell. It had already supported one oyster above the bottom, and its rough surface could support another. Shell recycling continues that same exchange by returning to the water what might otherwise leave the estuary as waste.
But replacing shell does not automatically rebuild a reef.
Loose shell may sink into soft sediment, scatter during storms, or become coated with mud before larvae arrive. Even after settlement, young oysters remain vulnerable to predators, boring sponges, poor water quality, burial, and the changing bottom beneath them (Daniel, 2015; Theuerkauf et al., 2015).
As those limits became clearer—and as clean shell became less available—restoration expanded to include marl, limestone, concrete, and manufactured structures. These materials do not replace oyster shell in every way, but their weight and shape may help them remain exposed where loose shell would sink or shift (Daniel, 2015; Theuerkauf et al., 2015).
Protected reefs and sanctuaries address a different loss. They give oysters time to grow, reproduce, die, and leave their shells where they settled. Over multiple generations, living oysters and empty shell can accumulate into the height and complexity that a newly planted surface does not yet possess (North Carolina Division of Marine Fisheries, 2022).
Aquaculture creates another kind of oyster landscape. Farms may raise oysters above the bottom in bags or cages, reducing some risks from burial and bottom-dwelling predators while producing a marketable crop. The oysters remain connected to the surrounding sound, but the structure is managed around growth and harvest rather than the long accumulation of shell within a natural reef (Kinsella, 2019).
The oysters grown there may be diploid, triploid, or selectively bred for traits such as faster growth, improved shell shape, summer body condition, or resistance to particular diseases. Those choices influence more than the oysters eventually harvested.
Triploid eastern oysters typically invest less energy in reproduction that diploids, often maintaining fuller body condition during warmer months while contributing fewer larvae to surrounding waters. | Image credit: Nell, 2002
Triploids devote far less energy to reproduction and usually contribute fewer larvae to surrounding waters. That can reduce the movement of farm-selected genetics into wild populations, but it also means that a farm containing many living oysters may contribute relatively little to the next generation settling beyond its cages. Selective breeding creates a different tradeoff. By choosing which oysters become broodstock, hatcheries repeatedly reproduce some traits while others present in the broader population are not carried forward in that line (Matt et al., 2025). If those cultured oysters are fertile, their larvae may mix with nearby wild populations and influence the genetic makeup of later generations (Varney et al., 2018).
A trait useful on a farm is not necessarily useful under every condition outside it. An oyster selected for rapid growth, shell shape, or survival against one disease may not be equally suited to burial, predators, storms, low salinity, or another disease on unmanaged bottom. Selection can strengthen a desired trait without preserving every form of variation that helps a wild population respond to an uncertain estuary (Matt et al., 2025).
A restored reef, a sanctuary, and an oyster farm may all place or protect oysters within the same estuary. They are not identical structures, and they do not ask oysters to serve the same purpose.
Cultch returns a place to settle. Heavier material helps that place remain exposed. Sanctuaries provide time for oysters and shell to accumulate. Recycling keeps old shell within the cycle. Aquaculture raises oysters above some hazards while supporting a working fishery.
Each approach returns something.
None returns everything an old reef contained.
Oysters growing near Soundside Park in Surf City, where reef structure, tidal exposure, sediment, and changing water conditions all shape what survives. | Image credit: A. Mitchell
A Coast That Does Not Hold Still
New River and Stump Sound have never been stationary places.
The same barrier-island processes that shape them today—shifting inlets, storms, tides, freshwater flow, erosion, and moving sediment—also surrounded the reefs that once produced New River’s “whopper” oysters. Channels changed, shell was buried and exposed, and salinity rose and fell long before oyster restoration began.
Yet those earlier reefs persisted.
Their stability did not come from an unchanging coast. It came from abundance. Large numbers of oysters spawned into the water, while generations of living and dead shell held parts of the reef above the mud. Losses in one season could be followed by settlement in another. A storm might damage one portion of a reef while exposing shell elsewhere. Enough adults, larvae, and hard surface remained for the structure to continue rebuilding itself.
That capacity changes as reefs become smaller, lower, or more widely separated.
A reduced reef produces fewer larvae and offers less exposed shell when those larvae are ready to settle. A newly planted reef may provide hard surface, but it does not immediately contain the height, age structure, reproductive adults, or accumulated generations of shell found in an older reef. It must develop those qualities while the estuary continues to move around it (North Carolina Division of Marine Fisheries, 2022; Theuerkauf et al., 2015).
Restoration does not begin after that movement has ended.
It happens inside it.
A successful settlement may be followed by storm-driven burial. Repeated rainfall may lower salinity, while drought can allow disease and saltwater predators to move farther upriver. Dredging or a shifting channel may alter the current carrying food and larvae across the reef. A sanctuary can prevent harvest, and heavier material may resist sinking, but neither can supply suitable water or guarantee that enough oysters will survive and reproduce (Ben-Horin et al., 2024; Ford & Tripp, 1996; Kinsella, 2019).
Oyster reef condition is measured by more than abundance alone. Reef height, extent, structural complexity, and the amount of shell retained all help determine how well a reef can persist and rebuild. | Image credit: NOAA Fisheries
This is why restoration does not move in a straight line from damaged to rebuilt. Its outcome depends not only on whether shell or another material was placed in the water, but on what develops there afterward: how many larvae arrive, which oysters reproduce, how much shell remains exposed, and whether the reef can begin replacing its own losses (North Carolina Division of Marine Fisheries, 2022; Theuerkauf et al., 2015).
At low tide, an old reef and a newly restored one may both appear to be fixed patches of shell.
The difference lies in what each can carry forward when the coast moves again.
Oyster farms can remove suspended algae and nutrients as oysters feed, but their benefits still depend on the water moving through the estuary around them. | Image credit: NOAA Fisheries
What the Shell Cannot Tell Us
An oyster growing along the edge of a creek does not look different when the water around it closes to harvest.
Its shell may remain tightly shut at low tide. It may continue feeding when the water returns, adding new growth along its edge and sharing the reef with oysters that appear equally healthy. Nothing visible in the animal tells us whether the surrounding water is approved for harvest, temporarily closed after heavy rain, part of a private lease, or prohibited from direct harvest altogether.
Those distinctions exist on maps rather than shells.
A healthy-looking oyster does not reveal whether the water around it is open to harvest or whether harmful bacteria or contaminants may be present. | Image credit: Chesapeake Bay Program
Shellfish-growing classifications reflect what may enter the water from the land around it: runoff, wastewater systems, marinas, shoreline development, rainfall, currents, and freshwater moving through the estuary. Some areas remain generally open. Others may be harvested only while certain conditions are met, and some remain closed because the risk of contamination is too great (Coulliette & Noble, 2008).
The oyster experiences the water itself, not the line drawn around it.
It may continue to grow in water from which people cannot safely gather it. Contaminants and naturally occurring bacteria do not always change its appearance, smell, or taste. A reef can therefore look alive and productive while the oysters growing there are not legally—or safely—available for someone walking past at low tide.
The old advice to eat oysters only during months containing the letter “R” cannot reveal those conditions either.
The saying reaches back to a time when cool weather made harvested oysters easier to store and transport before reliable refrigeration (Purvis, 2025). It also follows the seasonal life of wild diploid oysters, which use much of their stored energy for reproduction during warmer months and may become thinner or more watery after spawning. Triploid farmed oysters reproduce far less and may retain fuller bodies through summer (Bodenstein et al., 2023).
But the spelling of the month does not tell us where an oyster grew or what happened after it left the water.
Warm conditions increase concerns from naturally occurring Vibrio bacteria (Froelich & Noble, 2016), while heavy rainfall, wastewater failures, harmful algal blooms, and other contamination can affect shellfish waters in any season (Coulliette & Noble, 2008; Rolton et al., 2022). A legally harvested oyster from monitored water may be sold during a month without an “R.” An oyster gathered from closed water in January may still be unsafe (Coulliette & Noble, 2008; Purvis, 2025).
Vibrio vulnificus can occur naturally in coastal waters and may be present in oysters without changing how they look, smell, or taste. Image credit: Northwest Fisheries Science Center
What matters is less visible: where the oyster was harvested, whether that water was open at the time, the tag identifying the shellfish lot, and how quickly the oysters were cooled and handled (U.S. Food and Drug Administration, 2023).
A drifting larva cannot see any of those boundaries or classifications. It encounters water, sediment, predators, and whatever hard surface remains exposed when it is ready to settle.
Only later do people draw lines around the place where it stopped.
What the Reef Keeps
Eventually, the oyster dies.
Its soft body may be eaten or disappear after a predator opens the shell. The shell remains longer. Barnacles spread across it. A mud crab settles beneath one edge, while a small fish slips into the space between it and the next shell.
Waves may break it. Sediment may bury it. A storm may expose it again years later. It may leave the sound with a harvested oyster, return as recycled cultch, or remain where the animal spent its entire attached life.
If it stays within the reef, death changes the oyster’s role without ending it.
The living animal once fed, reproduced, and added new shell along its growing edge. The empty shell now helps hold the reef above the bottom, preserves shelter for other animals, and offers hard surface to larvae still drifting through the sound.
This is what connects the old New River oyster rocks, the shells carried away, the cultch returned, and the reefs still being restored and protected today. The modern oyster landscape has changed, but the next generation still depends upon the same inheritance.
A larva begins with nowhere to belong.
After weeks carried through water it cannot control, it reaches the reef and touches shell. The surface may belong to an oyster that died the previous summer. Beneath it may lie another shell worn by years of tides, and beneath that, fragments left by generations no one saw alive.
The larva cannot know how the reef began or what people have done to preserve it.
It only knows that the surface holds.
The drifting ends, and another life becomes fixed to the history beneath it.
At low tide, the reef may still look like the remains of something. Look closer, and there is no clean line between an ending and a beginning.
What one generation leaves changes what the next can become.
Living and empty oyster shells layered within an Onslow County marsh, where one generation’s remains may become the foundation for the next. | Image credit: A. Mitchell
References
Ben-Horin, T., Ciesielski, M., Lucas, J., Noble, R. T., & Wilbur, A. (2024). Pathology associated with summer oyster mortality in North Carolina. Aquaculture Reports, 34, 101901. https://doi.org/10.1016/j.aqrep.2023.101901
Bodenstein, S., Casas, S. M., Tiersch, T. R., & La Peyre, J. F. (2023). Energetic budget of diploid and triploid eastern oysters during a summer die-off. Frontiers in Marine Science, 10. https://doi.org/10.3389/fmars.2023.1194296
Claassen-MacClelland, C. P. (1979, November). Prehistoric occupation on the central and southern coast of North Carolina: Two hypotheses [Paper presentation]. Annual Meeting of the Southeastern Archaeological Conference, Atlanta, GA.
Coulliette, A. D., & Noble, R. T. (2008). Impacts of rainfall on the water quality of the Newport river Estuary (Eastern North Carolina, USA). Journal of Water and Health, 6(4), 473-482. https://doi.org/10.2166/wh.2008.136
Daniel, L. B. (2015, March). The N.C. experience: The history of oyster management over the past century [Paper presentation]. North Carolina Oyster Summit, North Carolina Coastal Federation, Raleigh, NC.
Ford, S. E., & Tripp, M. R. (1996). Diseases and defense mechanisms. In V. S. Kennedy, R. I. E. Newell, & A. F. Eble (Eds.), The eastern oyster: Crassostrea virginica (pp. 581-660). Maryland Sea Grant College.
Froelich, B. A., & Noble, R. T. (2016). Vibrio bacteria in raw oysters: Managing risks to human health. Philosophical Transactions of the Royal Society B: Biological Sciences, 371(1689), 20150209. https://doi.org/10.1098/rstb.2015.0209
Hillman, R. E., & Galtsoff, P. S. (1965). The American oyster, Crassostrea virginica Gmelin. Chesapeake Science, 6(3), 199. https://doi.org/10.2307/1350854
Kennedy, V. S. (1996). Biology of larvae and spat. In V. S. Kennedy, R. I. E. Newell, & A. F. Eble (Eds.), The eastern oyster: Crassostrea virginica (pp. 371-421). Maryland Sea Grant College.
Kennedy, V. S., E. Newell, R. I., & Eble, A. F. (1996). The eastern oyster: Crassostrea virginica. Maryland Sea Grant College.
Kinsella, J. D. (2019). Environmental effects on cultured oyster Crassostrea virginica: Implications for filtration capacity and production [Unpublished master’s thesis]. University of North Carolina Wilmington.
Matt, J. L., Small, J. M., Kube, P. D., & Allen, S. K. (2025). Quantitative genetic analysis of late spring mortality in triploid Crassostrea virginica. Genetics Selection Evolution, 57(1). https://doi.org/10.1186/s12711-025-00965-3
Mouchi, V., Andrus, C. F., Checa, A. G., Elliot, M., Griesshaber, E., Hausmann, N., Huyghe, D., Lartaud, F., Peharda, M., & De Winter, N. J. (2025). Oyster shells as archives of present and past environmental variability and life history traits: A multi‐disciplinary review of sclerochronology methods and applications. Limnology and Oceanography Letters, 10(2), 179-199. https://doi.org/10.1002/lol2.10461
North Carolina Geological and Economic Survey. (1911). Report of the fisheries convention held at New Bern, North Carolina, December 13, 1911. Edwards & Broughton Printing Company. https://digital.lib.ecu.edu/16832
North Carolina Geological Survey. (1887). Report on the waters of North Carolina, with reference to their possibilities for oyster culture. State of North Carolina. https://doi.org/10.5962/bhl.title.49874
Rolton, A., Rhodes, L., Hutson, K. S., Biessy, L., Bui, T., MacKenzie, L., Symonds, J. E., & Smith, K. F. (2022). Effects of harmful algal blooms on fish and shellfish species: A case study of New Zealand in a changing environment. Toxins, 14(5), 341. https://doi.org/10.3390/toxins14050341
Smith, S., Ciesielski, M., Clerkin, T., Ben-Horin, T., & Noble, R. T. (2025). Farmed oyster mortality follows consistent vibrio community reorganization. mSystems, 10(10). https://doi.org/10.1128/msystems.01078-25
Theuerkauf, S. J., Burke, R. P., & Lipcius, R. N. (2015). Settlement, growth, and survival of eastern oysters on alternative reef substrates. Journal of Shellfish Research, 34(2), 241-250. https://doi.org/10.2983/035.034.0205
U.S. Coast and Geodetic Survey. (1933). Descriptive report: Topographic survey sheets 4721–4725, New River, North Carolina (HT-113). U.S. Department of Commerce. https://www.ngs.noaa.gov/desc_reports/T04721.pdf
U.S. Food and Drug Administration. (2023). National Shellfish Sanitation Program (NSSP) Guide for the Control of Molluscan Shellfish 2023 Revision. https://www.fda.gov/media/181370/download
Varney, R. L., Watts, J. C., & Wilbur, A. E. (2018). Genetic impacts of a commercial aquaculture lease on adjacent oyster populations. Aquaculture, 491, 310-320. https://doi.org/10.1016/j.aquaculture.2018.03.060
Winslow, F. (1885). Report of the Waters of North Carolina with reference to their Possibilities for Oyster Culture. P. M. Hale.
Spend enough time walking along a salt marsh and you’ll eventually stop noticing the marsh rabbits.
Not because they’ve disappeared.
Because they’ve become part of the landscape.
They feed quietly along the marsh edge, slipping into the grasses when startled before appearing again somewhere you didn’t expect. Some evenings you may count half a dozen. Other days you wonder if there were ever any there at all.
Unlike the brighter cottontails many people are used to seeing, marsh rabbits are darker, with coarse brown to reddish-brown fur, a grayish underside, and a rusty cinnamon patch along the back of the neck. Even the tail gives them away. Instead of flashing bright white, it appears darker and more bluish, one reason marsh rabbits have sometimes been called “bluetails” (Chapman & Trani, 2007; Chapman & Willner, 1981).
Like so much of the marsh, they’re easy to overlook.
A marsh rabbit may look like a familiar backyard visitor, but its role reaches far beyond the grass beneath it. | Image credit: skylarkymalarkey, iNaturalist
For more than a century, naturalists have described marsh rabbits (Sylvilagus palustris) by documenting where they lived, what they looked like, and what they ate (Rhoads & Young, 1897). Those observations gave us our first understanding of the species. Today, ecology invites us to ask a different question.
What happens because marsh rabbits are here?
The answer reaches far beyond the rabbit itself.
We often measure an animal’s importance by how exciting it is to watch.
The marsh doesn’t.
The marsh measures importance by how many lives are connected to one another (Soulé et al., 2003).
Following One Rabbit
If you’ve ever taken a science class, you’ve probably learned the First Law of Conservation of Energy: energy cannot be created or destroyed. It only changes form.
For many of us, that idea remained in a textbook or written across a classroom whiteboard. It became something to memorize rather than something we expected to witness.
Yet every walk beside a salt marsh quietly brings that principle to life.
Standing beside a marsh, it’s easy to underestimate what you’re seeing. From a distance, much of it appears to be little more than grass. Yet every growing season those grasses capture enormous amounts of energy from the sun, making salt marshes among the most productive ecosystems on Earth (Frizzell, 1988).
That productivity, however, cannot remain in the plants.
It has to move.
Imagine following a single marsh rabbit through its life.
Following one marsh rabbit means following the grasses, cover, and hidden pathways that connect it to the larger marsh. | Image credit: jorgenols, iNaturalist
At only about 2.5 to 3.5 pounds, its small body holds energy gathered first by the marsh plants around it (Chapman & Trani, 2007; Chapman & Willner, 1981).The grasses it consumes become muscle, bone, blood, fur, and new life. That rabbit may one day feed a hawk, an owl, a fox, a bobcat, or a snake. Throughout its life it supports parasites. After its death it feeds scavengers, fungi, bacteria, and countless decomposers before eventually returning nutrients to the marsh where another season of growth begins.
Nothing has appeared from nowhere.
Nothing has truly disappeared.
The energy has simply changed form.
Every day, marsh rabbits transform marsh vegetation into something that can support an entirely different community of organisms (Chapman & Trani, 2007; Chapman & Willner, 1981).
The rabbit isn’t the end of the story.
In many ways, it’s where the story begins.
More Than a Meal
Spend a few minutes watching a marsh rabbit and it may not seem particularly busy.
It grazes along the marsh edge, pauses to listen, slips into dense cover, then returns to feeding when the danger seems to have passed. At first glance, it looks like a small animal moving through its day.
But even before a marsh rabbit becomes food for something else, it is already shaping the marsh around it.
Every bite influences which plants are grazed and which continue growing (Conner & Cherry, 2017). As it moves between the marsh edge, nearby cover, and slightly higher ground, the rabbit is also moving through the boundary between habitats most of us see as separate. The same dense vegetation that protects the rabbit also provides shelter for insects, reptiles, amphibians, birds, and countless other small lives moving through the marsh (Canepuccia et al., 2023; Larsen & Gray et al., 2021; Wigley & Lancia, 1998).
A marsh rabbit browses at the edge, where each ordinary bite helps move energy through the landscape. | Image credit: cadecampbell, iNaturalist
This is why the rabbit matters before the hawk ever appears.
Its value is not limited to becoming prey. Its ordinary life helps move energy, shape vegetation, and connect habitats long before that energy travels farther up the food web (Chapman & Trani, 2007; Chapman & Willner, 1981; Conner & Cherry, 2017).
Perhaps that is the quiet work of a marsh rabbit.
Not simply feeding something else.
But helping hold together the conditions that allow so much else to live there.
Why There Are So Many
Sometimes marsh rabbits seem to be everywhere — in yards, along road edges, near parking lots, and wherever the Spartina meets slightly higher ground.
A young marsh rabbit beside an adult shows the visible side of abundance, but reproduction is only part of the story. | Image credit: Wolfgang, iNaturalist
The easy explanation is that rabbits reproduce quickly. They can produce several litters in a year, often three to seven, with roughly 15 to 20 young produced annually under favorable conditions (Holler & Conaway, 1979).
That is true, but it is not the whole story.
Nature rarely invests heavily in something that does not matter. In a marsh, abundance is not waste. It is part of the system.
Marsh rabbits live under constant pressure. Every choice — where to feed, when to move, when to freeze, and when to disappear into the grasses — is shaped by predators, tides, weather, and the daily balance between finding food and becoming food (Hill et al., 2019; Holler & Conaway, 1979).
Predators influence far more than the animals they catch. Their presence can change where prey feed, how long they remain exposed, and how energy moves through the landscape (Suraci et al., 2019). When predator communities shift, those changes can ripple through the food web in ways that affect many other species (Bransford et al., 2024; Jiménez et al., 2019) .
Seen this way, abundant marsh rabbits are not simply evidence of successful reproduction.
They are evidence of how much work this one ordinary species performs.
The Rabbit You Didn’t See
Perhaps this also explains something you’ve probably noticed yourself.
One moment several marsh rabbits are feeding along the marsh edge.
You look away for only a moment.
When you look back, they’re gone.
They haven’t left the marsh.
Unlike many rabbits people are used to seeing, marsh rabbits are strong swimmers. Water is not simply something they avoid; it is part of the landscape they know how to use. In a place shaped by tides, wet ground, and narrow edges of cover, the ability to move through water helps explain how they can vanish so completely without ever leaving the marsh (Chapman & Trani, 2007; Chapman & Willner, 1981).
The same dense vegetation that feeds them also protects them. Slight changes in elevation, the rhythm of the tides, the angle of the evening sun, and generations of natural selection have shaped an animal that survives by knowing exactly when to be seen — and when not to be (Chapman & Willner, 1981; Holler & Conaway, 1979).
The rabbit disappeared from sight.
Its place in the marsh never did.
Looking at the Marsh Differently
The next time you notice a marsh rabbit quietly feeding along the marsh edge, pause before it disappears.
What once looked like an ordinary rabbit is now something entirely different.
Not because the rabbit has changed.
But because you can now see the countless connections passing through it (Soulé et al., 2003).
And once you see those connections, the marsh becomes harder to overlook.
A marsh rabbit slips back into the edge, leaving only a glimpse of the connections still moving through the marsh. | Image credit: maxnel, iNaturalist
References
Bransford, T. D., Harris, S. A., & Forys, E. A. (2024). Seasonal variation in mammalian Mesopredator spatiotemporal overlap on a barrier island complex. Animals, 14(16), 2431. https://doi.org/10.3390/ani14162431
Canepuccia, A. D., Fanjul, M. S., & Iribarne, O. O. (2023). Global distribution and richness of terrestrial mammals in tidal marshes. Diversity and Distributions, 29(5), 598-612. https://doi.org/10.1111/ddi.13683
Chapman, B. R., & Trani, M. K. (2007). Marsh Rabbit (Sylvilagus palustris). In The Land Manager’s Guide to Mammals of the South (pp. 247-251). Durham, NC: The Nature Conservancy; Atlanta, GA: U.S. Forest Service.
Conner, L. M., & Cherry, M. J. (2017). Considering Herbivory and Predation in Forest Management. In Ecological Restoration and Management of Longleaf Pine Forests (1st ed., p. 12). CRC Press.
Frizzell, E. K. (1988). Mammals and Wetlands. In The Ecology and Management of Wetlands: Volume 1: Ecology of Wetlands (1st ed., pp. 213-226). Croom Helm Ltd.; Timber Press.
Hill, J. E., DeVault, T. L., & Belant, J. L. (2019). Cause‐specific mortality of the world’s terrestrial vertebrates. Global Ecology and Biogeography, 28(5), 680-689. https://doi.org/10.1111/geb.12881
Holler, N. R., & Conaway, C. H. (1979). Reproduction of the marsh rabbit (Sylvilagus palustris) in South Florida. Journal of Mammalogy, 60(4), 769-777. https://doi.org/10.2307/1380192
Jiménez, J., Nuñez-Arjona, J. C., Mougeot, F., Ferreras, P., González, L. M., García-Domínguez, F., Muñoz-Igualada, J., Palacios, M. J., Pla, S., Rueda, C., Villaespesa, F., Nájera, F., Palomares, F., & López-Bao, J. V. (2019). Restoring APEX predators can reduce mesopredator abundances. Biological Conservation, 238, 108234. https://doi.org/10.1016/j.biocon.2019.108234
Larsen-Gray, A. L., Loeb, S. C., & Kalcounis-Rueppell, M. C. (2021). Rodent population and community responses to experimental, large scale, long-term coarse Woody debris manipulations. Forest Ecology and Management, 496, 119427. https://doi.org/10.1016/j.foreco.2021.119427
Macarthur, R., & Levins, R. (1967). The limiting similarity, convergence, and divergence of coexisting species. The American Naturalist, 101(921), 377-385. https://doi.org/10.1086/282505
Rhoads, S. N., & Young, R. T. (1897). Notes on a Collection of Small Mammals from Northeastern North Carolina. Proceedings of the Academy of Natural Sciences of Philadelphia, 49, 303-312. https://www.jstor.org/stable/4062279?seq=1
Soulé, M. E., Estes, J. A., Berger, J., & Del Rio, C. M. (2003). Ecological effectiveness: Conservation goals for interactive species. Conservation Biology, 17(5), 1238-1250. https://doi.org/10.1046/j.1523-1739.2003.01599.x
Suraci, J. P., Clinchy, M., Zanette, L. Y., & Wilmers, C. C. (2019). Fear of humans as APEX predators has landscape‐scale impacts from mountain lions to mice. Ecology Letters, 22(10), 1578-1586. https://doi.org/10.1111/ele.13344
Wigley, T. B., & Lancia, R. A. (1998). Wildlife Communities. In Southern Forested Wetlands (1st ed., p. 32). Routledge.
A reader recently asked me about five birds he had seen over the sounds of Surf City last weekend. He was convinced they were five different kinds of “sea hawks.”
At first glance, it was an understandable conclusion.
Each bird was large. Each spent time soaring overhead or hesitating up high over the water. Each occupied the same stretch of coastal North Carolina sky.
Yet every photograph and description reflected the same species: an osprey.
Distance has a way of simplifying wildlife. Colors disappear. Markings fade. Details are lost. What remains is a silhouette against the sky.
Most of us learn to recognize birds by their appearance. Raptors are often easier to understand by their behavior.
What is the bird doing?
Is it hovering over the water?
Circling without flapping?
Perched motionless on a fence post?
Drifting above a marsh?
Crossing silently through the trees after sunset?
The answer often reveals more than the feathers.
The skies above Onslow County are shared by a community of predators. Some hunt fish. Some hunt rodents. Some hunt insects. Some hunt other birds. Some hunt only at night. Others serve as nature’s cleanup crew.
At a distance they may look similar.
Spend enough time watching them, however, and the differences become impossible to miss.
Following the Fish
Osprey: The Fisherman
If there is a signature bird of the coast, it may be the osprey (Pandion haliaetus).
You notice one long before you identify it. The bird appears above a creek, river, or stretch of open water, turns into the wind, and suddenly seems to stop moving. For a few seconds it hangs there, suspended above the surface before plunging feet-first toward the water below.
That moment of hesitation is not hesitation at all.
The bird is making a final decision.
Water distorts light. Fish change direction. Wind roughens the surface. What appears obvious from a dock or kayak becomes much more complicated from above. The osprey’s brief hover allows it to judge distance, depth, and movement before committing to the dive (Poole, 1989; Bierregaard et al., 2020).
The splash usually draws everyone’s attention.
The fish often draws the next question.
Watch an osprey leave the water carrying a mullet or menhaden and it is difficult not to wonder how the bird manages to hold onto it. Fish are essentially living bars of soap wrapped in muscle, built to slip through water and escape predators. Osprey solve that problem with feet lined by tiny backward-facing spicules and a reversible outer toe that help secure slippery prey (Poole, 1989; Bierregaard et al., 2020).
Then, almost as soon as the bird becomes airborne, something else happens.
The fish turns.
Within seconds the osprey has repositioned its catch so the fish faces forward. What looks like a small adjustment saves energy over the course of the flight. A fish carried sideways catches air. A fish carried headfirst moves through it. Often the bird gives its catch a vigorous shake as it climbs away from the water, shedding excess water before continuing on its way. Together, these adjustments reduce drag and make transporting a heavy, slippery meal through the air more efficient (Allen et al., 2018; Poole, 1989; Bierregaard et al., 2020).
Around nesting season, however, it is often the noise rather than the fishing that gets people’s attention.
Osprey rarely seem quiet.
Calls echo from nesting platforms, channel markers, dead trees, and utility poles throughout the breeding season. Adults announce arrivals. Mates communicate with one another. Young birds call constantly whenever food appears nearby. What sounds chaotic from a distance is often a family carrying on a conversation (Bierregaard et al., 2020).
By late summer, that family becomes easier to see.
Several birds may gather near a nest, perched along the same stretch of water where they have spent months raising young. Then, without warning, they take to the air together. The younger birds follow the adults across creeks, marshes, and open water, practicing turns, landings, and the flight skills that will eventually carry them south. What appears at first to be a loose gathering of osprey is often a family still learning from one another long after the young birds have left the nest (Poole, 1989; Bierregaard et al., 2020).
To boaters, it is a channel marker in the New River in Jacksonville, NC. To an osprey, it is home. Many coastal nests are rebuilt and expanded year after year, becoming landmarks visible across the water. | Image credit: A. Mitchell
The nests themselves remain long after the birds have departed.
Many osprey return to the same sites year after year, adding sticks, repairing damage, and expanding structures that can eventually become enormous. What begins as a modest nest slowly grows into a landmark visible from hundreds of yards away (Poole, 1989; Bierregaard et al., 2020).
For many coastal residents, those nests become part of the landscape.
And when spring returns, so do the birds that built them.
Bald Eagle: The Opportunist
If you spend enough time around the water, eventually you’ll see it happen.
An osprey leaves the surface carrying a fish. For a few moments, everything appears normal. Then a second bird enters the scene.
Larger.
Heavier.
Built on an entirely different scale.
The bald eagle (Haliaeetus leucocephalus) begins to follow.
What started as a successful fishing trip suddenly becomes a chase.
From below, the interaction can look almost personal. The osprey twists and climbs. The eagle closes the distance. Sometimes the osprey escapes. Sometimes it drops the fish. The eagle wheels downward after the falling meal while the osprey continues on empty-taloned.
Why go through all that trouble?
Because catching a fish requires energy.
An osprey may spend considerable time searching the water, hovering above the surface, adjusting for currents, and committing to a dive before finally securing a meal. An eagle watching from a nearby perch can recognize that success immediately. From the eagle’s perspective, the fish has already been found. The difficult part of the hunt is over (Buehler, 2020).
This often leads people to wonder whether bald eagles are better fishermen than osprey.
The answer depends on how you define fishing.
If the goal is catching fish, the osprey remains the specialist. Nearly every aspect of its anatomy is designed around that task. Its feet grip slippery prey with remarkable efficiency, and its entire hunting strategy revolves around locating fish beneath the water’s surface.
A bald eagle approaches the world differently.
Rather than specializing in a single food source, eagles take advantage of opportunities wherever they find them. Fish remain important, particularly along the New River, Stump Sound, the Intracoastal Waterway, and the countless creeks that thread through coastal marshes. Yet waterfowl, mammals, reptiles, and carrion can also become part of the menu (Buehler, 2020).
A closer look at their feet reveals those differences. Osprey feet are designed to hold fish. Eagle talons are designed to seize and restrain a wider variety of prey. One bird is built around precision. The other is built around versatility (Buehler, 2020).
That versatility helps explain why bald eagles have become increasingly common sights along the Onslow County coast. Open water, abundant prey, expansive marshes, and large trees provide everything they need. Whether soaring above an estuary, perched along a creek, or watching from a pine overlooking the water, eagles occupy a position near the top of the coastal food web (Buehler, 2020).
And every so often, that position allows them to let someone else do the fishing.
The Hunters of Marsh and Forest
Red-shouldered Hawk: The Watcher on the Fence
Not every raptor announces itself from the sky.
Some introduce themselves by showing up in the yard.
You glance out the window and notice a hawk perched on the fence. Hours later it seems to be in exactly the same place. The next morning it is back again.
Eventually curiosity takes over.
What is it watching?
Perched above a yard in Jacksonville, NC, a red-shouldered hawk waits for movement. From elevated vantage points, these woodland hunters watch patiently for opportunities hidden within the landscape below. | Image credit: A. Mitchell
Many people assume the hawk is focused on the house, the dog, or the family moving through the yard.
In reality, the bird is usually paying attention to everything else.
A well-maintained yard often provides excellent hunting habitat. Frogs move through flower beds. Lizards bask along retaining walls. Small snakes hunt beneath shrubs. Mice travel fence lines and wood piles. The red-shouldered hawk watches for movement, waiting for the landscape to reveal itself (Dykstra et al., 2020).
That patient approach reflects the habitats these birds prefer.
Unlike the open-country red-tailed hawk, red-shouldered hawks (Buteo lineatus) are closely tied to places where woods and water meet. Creek corridors, swamp edges, ponds, marshes, and bottomland forests provide the cover and diversity of prey they rely upon (Dykstra et al., 2020).
A red-shouldered hawk feeds on captured prey in a parking lot. While often associated with swamps and wooded wetlands, these adaptable hunters frequently take advantage of opportunities in suburban landscapes. | Image credit: A. Mitchell
Along the coast, those habitats frequently overlap with where people live.
The fence post is simply the best seat in the house.
From there, the hawk can watch an entire ecosystem unfold beneath it.
Red-tailed Hawk: Master of the Open Sky
A red-tailed hawk (Buteo jamaicensis) – and my personal favorite bird – often attracts attention by doing remarkably little.
You notice one circling high above a field.
Several minutes later it is still there.
The wings barely move.
At first, most people wonder how the bird can remain in the air for so long without flapping. The answer lies in the atmosphere itself. As the ground warms, pockets of heated air rise into the sky. Red-tailed hawks locate these invisible thermals and circle within them, gaining altitude while expending very little energy (Kerlinger, 1989; Preston & Beane, 2024).
But staying aloft is only part of the story.
The real question is why the bird wants to be up there in the first place.
The answer becomes clearer when compared to the red-shouldered hawk.
A red-shouldered hawk often hunts by focusing on a particular place. A pond edge. A marsh creek. A backyard. It watches patiently from a perch, waiting for the landscape to reveal movement (Dykstra et al., 2020).
A red-tailed hawk takes the opposite approach.
Rather than concentrating on one corner of the landscape, it climbs high enough to see how all of those pieces connect. Fields blend into hedgerows. Roadsides meet forest edges. Open ground transitions into cover. From above, what appear to be separate places from the ground become a single hunting landscape.
That broader view is the red-tail’s specialty.
What appears to us as an empty field is filled with clues. A rabbit pauses along a fence line. A squirrel breaks from cover. A mouse rustles through the grass. The bird is not searching for a specific animal. It is searching for movement, patterns, and opportunities spread across hundreds of acres (Preston & Beane, 2024).
The thermal keeps the hawk aloft long enough to gather that information. Height becomes an advantage. Distance becomes information.
The bird is not circling because it has nowhere else to be.
It is circling because the sky offers the best view.
And from that vantage point, one movement in the wrong place at the wrong time is often all it takes.
Cooper’s Hawk: The Pursuit Hunter
If you maintain a bird feeder long enough, sooner or later the yard will go silent.
One moment cardinals, doves, and finches are moving between the feeder and nearby trees.
The next, everything disappears.
Then a gray blur streaks through the yard.
The first time you see it happen, it feels almost impossible that a bird that large could move that quickly through such a cluttered space.
Unlike the red-tailed hawk searching from hundreds of feet above the landscape or the red-shouldered hawk watching patiently from a perch, the Cooper’s hawk (Astur cooperii) hunts in motion. It is built for pursuit (Rosenfield et al., 2025).
Its long tail acts like a rudder while relatively short wings allow it to twist, turn, and accelerate through spaces that would seem impossible for most raptors. Branches, fences, shrubs, and backyard obstacles that slow other birds become part of the chase (Rosenfield et al., 2025).
That agility allows the hawk to exploit something many predators cannot.
Confusion.
A flock of birds startled into flight rarely moves in a straight line. Individuals scatter in different directions, darting through vegetation and searching for cover. The Cooper’s hawk follows.
What appears chaotic to us is a hunting opportunity to the hawk.
Yet not every backyard attracts a Cooper’s hawk.
If you’ve ever noticed that these birds seem more common in some neighborhoods than others, the surrounding landscape is often the reason. Cooper’s hawks favor places where trees, forest edges, wooded corridors, and open spaces meet. Those transitions provide both cover and opportunity, allowing the bird to move quickly between concealment and pursuit (Rosenfield et al., 2025).
A bird feeder placed within that landscape can become part of the story, not because the feeder attracts the hawk, but because it concentrates movement. Birds travel between the feeder and nearby cover. The hawk is already watching the area. The feeder simply makes activity easier to find.
Which is why the sudden silence is often the first clue.
Long before most people see the hawk, the birds have already noticed it.
For a few moments, the yard belongs to the fastest hunter in the neighborhood.
The Hunters of the Air
Mississippi Kite: Catching the Wind
At first glance, a Mississippi kite (Ictinia mississippiensis) looks like it should behave like any other hawk.
It drifts overhead with long, pointed wings, barely moving as it rides the summer air. Then it suddenly changes direction, banking sharply, twisting through the sky, and accelerating after something too small for most people to see.
The first time you notice it, the behavior feels strange.
What is that hawk chasing? Is it chasing dragonflies?
The bird banks again, then again, each turn seeming impossibly precise. Whatever it is pursuing appears far too small to interest a raptor. Yet the longer you watch, the clearer the answer becomes.
While many hawks spend their time searching the ground for prey, Mississippi kites have turned the air itself into a hunting ground. Dragonflies, cicadas, beetles, and other flying insects become meals captured directly on the wing. What appears to be effortless wandering is often an active hunt unfolding overhead (Parker, 2020).
That hunting style explains why they seem so different from other raptors.
The red-shouldered hawk watches a particular place. The red-tailed hawk surveys an entire landscape. The Cooper’s hawk chases prey through trees and backyards. The Mississippi kite is hunting somewhere entirely different.
Its long wings and graceful flight allow it to maneuver with remarkable precision, changing direction quickly as insects dart, climb, and shift with the wind (Parker, 2020).
The same warm air currents that help other raptors gain altitude also gather flying insects into concentrated pockets, creating opportunities for a predator adapted to exploit them (Parker, 2020).
The result is a bird that often feels more like a swallow than a hawk.
An osprey may be hunting fish below. A red-tailed hawk may be watching a field nearby. A Cooper’s hawk may be moving along a forest edge. Above them all, a Mississippi kite may be feeding on insects carried by the same air currents that support the rest of the ecosystem.
The bird is not ignoring the landscape beneath it.
It has simply found opportunity in a place most predators never think to look.
For the Mississippi kite, the sky is not a pathway.
It is habitat.
The Cleanup Crew
Turkey Vulture: Death Becomes Renewal
A turkey vulture (Cathartes aura) lands on your roof and suddenly everyone becomes concerned.
To us, it looks like a warning. To the vulture, it is simply another perch from which to read the landscape. | Image credit: A. Mitchell
Some people take it as a bad omen. Others wonder if something nearby has died. Before long, the bird becomes the center of attention despite doing little more than sitting still.
The turkey vulture, meanwhile, is completely unaware of the stories being told about it.
Most of the time, something far less dramatic is happening.
A rooftop provides warmth on a cool morning, a place to dry rain-soaked feathers, or a convenient perch where rising air currents can be reached without much effort. The bird is not predicting death. It is simply taking advantage of the landscape (Kirk & Mossman, 2020).
Yet the association exists for a reason.
Unlike the hawks and eagles we have encountered so far, turkey vultures are searching for something very different. They are not looking for prey. They are looking for what remains after life has already moved on.
A dead fish along the shoreline.
A raccoon hidden in roadside vegetation.
A deer beyond the edge of a forest.
But how do they find it?
Part of the answer can be seen on the bird’s face. If you are fortunate enough to observe a turkey vulture through binoculars or at close range, you may notice something unusual about its nostrils, or nares. Unlike our own noses, the openings pass completely through the beak. In the right light, you can literally see from one side of the nostril to the other (Kirk & Mossman, 2020).
A close comparison of a turkey vulture (top) and black vulture (bottom) reveals one clue to how they read the landscape differently. Turkey vultures use an exceptional sense of smell to locate carrion, while black vultures depend more on vision and the behavior of other vultures. Arrows highlight differences in the nostril openings of the two species. | Image credit: T. Lisney
That adaptation supports one of the most powerful senses of smell in the bird world. While many raptors rely primarily on vision, turkey vultures are able to detect the scent of carrion from remarkable distances, allowing them to locate food sources hidden beneath vegetation and, in some cases, even beneath the soil itself (Grigg et al., 2017; Kirk & Mossman, 2020).
Finding carrion, however, is only part of the challenge.
Consuming it presents an entirely different set of problems.
The turkey vulture’s bald head, which many people find unsettling, is actually an important adaptation. Unlike a feathered head that could trap blood, bacteria, and other organic material, the bare skin can be cleaned much more easily after feeding. What gives the bird its ominous appearance also helps protect it from the very things it eats (Roggenbuck et al., 2018).
The same is true inside the bird.
Turkey vultures possess an extraordinarily acidic digestive system capable of destroying many of the bacteria and pathogens that would make other animals sick. Organisms responsible for diseases such as anthrax, botulism, cholera, and salmonella are often neutralized during digestion, allowing the vulture to safely consume material that would be dangerous for most scavengers (DeVault et al., 2016; Kirk & Mossman, 2020).
Even their hygiene is unusual.
Turkey vultures practice a behavior known as urohidrosis, in which they defecate on their own legs. While it may seem unpleasant from a human perspective, the highly acidic waste helps kill bacteria picked up while walking on carcasses and also provides a cooling effect during hot weather (Arad et al., 1989; Kirk & Mossman, 2020).
Taken together, these adaptations solve a difficult ecological problem. Dead animals can become reservoirs for bacteria, disease, and decay. Turkey vultures have evolved to exploit that resource while avoiding many of the risks associated with it.
Black vultures, which are often seen alongside them, approach the problem differently. Their nostrils are narrower and not open from side to side. Rather than relying so heavily on smell, they depend more on vision and often watch the movements of turkey vultures to help locate food (Buckley et al., 2020).
That relationship creates an interesting partnership. Turkey vultures are often the first to detect a carcass hidden beneath vegetation, while black vultures are quick to notice where the turkey vultures are gathering. One species excels at finding the scent. The other excels at finding the finder (Buckley et al., 2020; Kirk & Mossman, 2020.
Together, the two species accomplish something few other animals can.
They return nutrients to the landscape.
What appears to be an ending becomes the beginning of something else. Energy stored within a fish, a raccoon, or a deer does not simply disappear. Vultures help move those nutrients back into the ecosystem where they become available to countless other organisms (DeVault et al., 2016) .
The bird on your roof is not waiting for something bad to happen.
More often than not, it is part of the reason the landscape remains healthy after it does.
Black Vulture: Following the Leader
A single turkey vulture on a rooftop often attracts attention.
Ten vultures attract concern.
What appears to be a crowd is often an information network. Black vultures frequently roost together, sharing a landscape where opportunities can appear and disappear without warning. | Image credit: jspruill, iNaturalist
Unlike turkey vultures, which are frequently seen soaring alone or in small numbers, black vultures (Coragyps atratus) often seem to arrive as a group, called a committee. One bird becomes five. Five become ten. Before long, an entire rooftop, parking lot, or dead tree appears covered in vultures (Buckley et al., 2020).
The first question is usually the same.
Why are there so many?
Part of the answer lies in how black vultures find food.
While turkey vultures rely heavily on their extraordinary sense of smell, black vultures depend much more on vision and on one another. They watch the landscape, but they also watch other vultures. A turkey vulture dropping toward a hidden carcass can reveal an opportunity that a black vulture might never have discovered on its own (Buckley et al., 2020).
That difference creates an unusual relationship between the two species.
Turkey vultures are often the first to locate carrion concealed beneath vegetation or hidden from view. Black vultures are often the first to notice that the turkey vultures have found something worth investigating (Buckley et al., 2020).
One species excels at finding the scent.
The other excels at finding the finder.
Their social nature extends beyond feeding. Black vultures frequently roost together, travel together, and gather in numbers that can seem surprising to people unfamiliar with them. What appears to be a crowd is often a network of birds sharing information about a landscape filled with unpredictable opportunities (Buckley et al., 2020).
That strategy has served them well.
A dead fish washed onto a shoreline, a raccoon along a roadside, or a deer hidden beyond the edge of a forest represents a resource that appears without warning and disappears quickly. By paying attention to one another, black vultures can exploit those opportunities efficiently.
To most people, the meal is something to avoid. To a black vulture, it is an opportunity. By consuming carrion that would otherwise decay on the landscape, vultures help return nutrients to the ecosystem while reducing the spread of disease. | Image credit: A. Mitchell
Like the turkey vulture, the black vulture plays an important role in returning nutrients to the ecosystem.
It simply approaches the problem differently.
Where the turkey vulture trusts its nose, the black vulture trusts its neighbors.
The Night Shift
As daylight fades, a different group of predators takes over.
The thermals weaken. The soaring hawks settle. Shadows lengthen across marshes and forests.
Then the owls emerge.
Eastern Screech-Owl: Master of Camouflage
Many people have an eastern screech-owl (Megascops asio) living in their neighborhood and never realize it.
Not because the owl is rare.
Because it is exceptionally good at remaining unnoticed.
You might spend years walking past the same tree without ever seeing this small bird tucked inside a cavity or pressed against the bark. Then one evening, just after sunset, a soft trill or whinny drifts through the yard and suddenly you realize there has been an owl nearby the entire time (Gehlbach, 2009; Ritchison et al., 2020).
The discovery often raises an interesting question.
If eastern screech-owls feed on many of the same insects, rodents, reptiles, and amphibians as some daytime raptors, why don’t we see them more often? (Gehlbach, 2009; Ritchison et al., 2020)
Part of the answer is timing.
While hawks spend the day watching fields, marshes, forests, and backyards, the eastern screech-owl waits for darkness. As daylight fades and the daytime hunters settle into roosts, the owl begins its own shift (Ritchison et al., 2020).
But timing alone does not explain its success.
The owl’s real advantage is concealment.
Its mottled gray and brown feathers blend remarkably well with tree bark, allowing it to disappear into the landscape even when it is in plain sight. During the day, many spend hours motionless inside tree cavities or against trunks where they become nearly impossible to detect (Gehlbach, 2009; Ritchison et al., 2020).
That camouflage allows the owl to remain close to people while largely escaping notice.
Neighborhoods, wooded lots, parks, forest edges, and suburban backyards can all provide suitable habitat. The insects drawn to porch lights, the rodents moving along fence lines, and the small reptiles hiding among shrubs create hunting opportunities throughout the night (Gehlbach, 2009; Ritchison et al., 2020).
By the time most people realize an eastern screech-owl is nearby, it has often been there all along.
Its success does not come from being the largest predator in the landscape.
It comes from being the one you never knew was watching.
Barn Owl: Sound Becomes Sight
A pale shape crosses a field at dusk.
For a moment it hardly seems real. The bird appears almost white against the fading light, gliding silently above the grass before disappearing into the darkness beyond.
The first question is often simple.
What did I just see?
For centuries, encounters like that have inspired stories of ghosts, spirits, and things that move through the night unseen. The barn owl’s piercing scream has only reinforced that reputation. Unlike the familiar hoots people associate with owls, barn owls produce calls that can sound startlingly human, often described as shrieks, screams, or cries drifting through the darkness. Heard for the first time from a forest edge or old barn, it is easy to understand how the bird became woven into folklore (Marti et al., 2024).
Yet the call serves a practical purpose.
In darkness, sound becomes one of the most effective ways for Americanbarn owls (Tyto alba pratincola) to communicate with mates, defend territories, and maintain contact with one another. What sounds eerie to us is simply part of life for an owl that spends most of its time hunting when the rest of the landscape is asleep (Marti et al., 2024).
The hunt itself is equally remarkable.
Barn owls are among the most specialized rodent hunters in North America. Their heart-shaped facial disks act like satellite dishes, funneling sound toward asymmetrical ears capable of pinpointing prey with astonishing precision. A mouse rustling through grass can reveal its location long before the owl ever sees it (Payne, 1971; Marti et al., 2024).
That adaptation helps explain another common experience.
Step quietly into an old barn, abandoned building, or large outbuilding and you may discover one or more barn owls perched overhead. They often watch intruders with an intense stare, swaying and bobbing from side to side as they study the unfamiliar visitor below (Marti et al., 2024).
At first glance, the behavior appears nervous or even strange.
In reality, the owl is gathering information. The subtle movements help it judge distance, depth, and position before deciding whether to remain still or slip silently into the darkness.
Fields, agricultural landscapes, marsh edges, and open grasslands provide ideal hunting habitat (Marti et al., 2024). Every mouse captured represents energy transferred from one part of the ecosystem to another, helping regulate populations that might otherwise grow unchecked.
Youtube:
The pale bird crossing the field is not a ghost.
It is one of the most effective hunters the night shift has to offer.
For the barn owl, sound does not simply reveal the landscape.
It becomes a way of seeing it.
Barred Owl: The Voice of the Swamp
“Who cooks for you? Who cooks for you-all?”
Once you hear it, you rarely forget it.
The call drifts through wooded neighborhoods, swamp edges, and forested wetlands after sunset, often carrying much farther than people expect. Many coastal residents know the sound long before they ever see the bird responsible for making it (Bierregaard et al., 2025).
The question naturally follows.
Who is calling from the darkness?
More often than not, it is a barred owl.
Unlike the barn owl crossing open fields or the eastern screech-owl disappearing into a backyard tree, barred owls (Strix varia) are closely tied to forests and wetlands. Swamps, creek corridors, bottomland hardwoods, and wooded neighborhoods provide the cover, water, and diversity of prey they need (Bierregaard et al., 2025).
The call itself serves several purposes. Barred owls use it to communicate with mates, establish territories, and maintain contact across dense forests where visibility is limited. What sounds like a conversation to us is often exactly that (Bierregaard et al., 2025).
Those forests and wetlands provide hunting opportunities throughout the year. Frogs call from wetland edges. Crayfish move through shallow water. Rodents travel beneath fallen leaves. Snakes, insects, and small birds all become potential prey. Rather than specializing in a single food source, barred owls have learned to take advantage of whatever the swamp provides (Bierregaard et al., 2025).
The swamp, however, does not make hunting easy.
Prey hides beneath vegetation, beneath water, and beneath layers of leaf litter. Fallen logs, tangled branches, and dense understory create countless places to disappear.
Barred owls overcome many of those challenges through silence.
The leading edges of their feathers are specially adapted to break up airflow, reducing the sound of flight to nearly nothing. A mouse rustling beneath leaves, a frog moving along a wetland edge, or a crayfish crossing shallow water may never hear the owl approaching (Bachmann & Wagner, 2016).
For prey, the danger often arrives without warning.
By the time a barred owl commits to an attack, silence has already done much of the work.
That ability helps explain why barred owls are among the most successful predators in the region.
It also reveals something many people do not realize.
Hunting is not simply a switch that turns on when a young owl leaves the nest.
Juvenile barred owls must learn. They practice. They miss opportunities. They refine the skills needed to locate, pursue, and capture prey in a complex environment. In wildlife rehabilitation settings, young barred owls that fail to develop those hunting skills cannot be successfully returned to the wild (Watson et al., 2023).
Instinct provides the foundation.
Experience builds the hunter.
Perhaps that is why barred owls have become such a familiar voice in the coastal night. Their success comes not from mastering a single prey species or hunting strategy, but from learning to adapt to whatever the swamp provides.
For the barred owl, the swamp is more than habitat.
It is a hunting ground, a classroom, and a home.
Great Horned Owl: Ruler of the Night
The night can be surprisingly noisy.
A barred owl calls from the swamp.
Tree frogs answer from the wetlands.
Crickets fill the spaces in between.
Then, sometimes, the woods erupt with alarm calls.
Crows mob during the day. Smaller birds call from hidden roosts after sunset. Even other predators seem suddenly aware that something has changed.
What happened?
Often, a great horned owl (Bubo virginianus) has arrived.
While many predators spend their lives worrying about what might hunt them, the great horned owl occupies a different position in the food web. Rabbits, squirrels, rodents, reptiles, birds, and even other predators can become prey. Where great horned owls occur, few animals completely ignore them (Artuso et al., 2020).
That includes other owls.
Barred owls, screech-owls, and other nocturnal hunters may alter their behavior when a great horned owl is nearby (Artuso et al., 2020). The question is not simply what the owl is hunting.
The question is whether anything wants to become its next opportunity.
Part of that success comes from versatility. Great horned owls hunt forests, wetlands, agricultural fields, suburban neighborhoods, and coastal habitats with equal confidence. Rather than specializing in a single prey species, they take advantage of whatever opportunities the landscape provides (Artuso et al., 2020).
Yet versatility alone does not explain why other animals react when one arrives.
Power does.
A great horned owl’s grip rivals that of a bald eagle. The force generated by its talons can exceed 270 newtons, allowing it to seize and control prey with remarkable efficiency (Ward et al., 2002). Those feet are capable of exerting tremendous force once they close around a target (Ward et al., 2002; Lingham-Soliar, 2014).
Combined with a wingspan approaching five feet, the result is a predator that commands attention even before it leaves the ground (Artuso et al., 2020).
Yet perhaps the most remarkable thing about a great horned owl is how quietly all of that power moves through the landscape.
Like other owls, the leading edges of their feathers break up airflow, reducing the sound of flight to nearly nothing. A bird carrying a wingspan wider than many people are tall can pass overhead with little more than a faint rush of air (Bachmann & Wagner, 2016).
Sometimes not even that.
The first indication that a great horned owl is nearby is often the reaction of everything else around it.
That silence becomes even more effective when paired with another adaptation.
Many people believe owls can rotate their heads completely around.
They cannot.
A great horned owl can rotate its head roughly 270 degrees, allowing it to scan much of the landscape without moving its body (Ward et al., 2002). Unlike our eyes, an owl’s eyes are largely fixed within the skull. To change its view, it must move its head (Ward et al., 2002; Lingham-Soliar, 2014).
For an ambush predator, that matters.
Every movement risks revealing its position. The ability to gather information while remaining nearly motionless allows the owl to watch far more than most animals realize.
And that may be the real reason so many creatures react when one arrives.
The great horned owl combines strength, silence, patience, and awareness in a way few predators can. By the time a rabbit, squirrel, snake, or even another owl realizes it is being watched, the great horned owl has often been watching for quite some time.
Perhaps that is why other animals seem to know when one is nearby.
The great horned owl is not simply another hunter in the night.
It is often the hunter watching the hunters.
Reading the Sky
At first glance, they all appear similar.
Large birds.
Broad wings.
Silhouettes against the sky.
Yet an osprey hovering above the water, a red-shouldered hawk watching from a fence post, a Mississippi kite chasing dragonflies, a vulture riding a thermal, and a barred owl moving through the darkness are not performing the same job.
They are reading the landscape in different ways.
The osprey watches the water.
The red-tailed hawk watches entire fields.
The Cooper’s hawk watches movement between trees.
The Mississippi kite watches the air itself.
Even the vultures, often dismissed as scavengers, are searching for clues that most of us never notice.
The next time a large bird catches your attention, resist the urge to identify it immediately.
Instead, watch what it does.
Does it hover?
Circle?
Perch?
Glide?
Disappear into the trees?
The answer often tells you as much as the feathers.
Because the sky is not filled with birds doing the same thing.
It is filled with specialists solving different problems.
And once you begin to notice those differences, the sky becomes a little easier to read.
At a distance, every raptor can seem like little more than a shape against the clouds. Spend enough time watching, however, and the sky becomes easier to read. | Image credit: A. Mitchell
References
Allen, L. L., Morrison, K. L., Scott, W. A., Shinn, S., Haltiner, A. M., & Doherty, M. J. (2018). Differences between stance and foot preference evident in osprey (Pandion haliaetus) fish holding during movement. Brain and Behavior, 8(11). https://doi.org/10.1002/brb3.1126
Arad, Z., Midtgard, U., & Bernstein, M. H. (1989). Thermoregulation in Turkey vultures. Vascular anatomy, arteriovenous heat exchange, and behavior. The Condor, 91(3), 505. https://doi.org/10.2307/1368103
Artuso, C., Houston, C. S., Smith, D. G., & Rohner, C. (2020). Great Horned Owl (Bubo virginianus). In Birds of the World (1.0th ed.). Cornell Lab of Ornithology.
Bierregaard, R. O., Livezey, K. B., Pyle, P., Mazur, K. M., & James, P. C. (2025). Barred Owl (Strix varia). In Birds of the World (2.1st ed.). Cornell Lab of Ornithology.
Bierregaard, R. O., Poole, A. F., Martell, M. S., Pyle, P., & Patten, M. A. (2020). Osprey (Pandion haliaetus). In Birds of the World (1.0th ed.). Cornell Lab of Ornithology.
Buckley, N. J., Kluever, B. M., Driver, R., & Rush, S. A. (2020). Black Vulture (Coragyps atratus). In Birds of the World (2.0th ed.). Cornell Lab of Ornithology.
Buehler, D. A. (2022). Bald Eagle (Haliaeetus leucocephalus). In Birds of the World (2.0th ed.). Cornell Lab of Ornithology.
DeVault, T. L., Beasley, J. C., Olson, Z. H., Moleón, M., Carrete, M., Margalida, A., & Sánchez-Zapata, J. A. (2016). Ecosystem Services Provided by Avian Scavengers. In Why Birds Matter: Avian Ecological Function and Ecosystem Services (pp. 235-270). University of Chicago Press.
Dykstra, C. R., Hays, J. L., & Crocoll, S. T. (2020). Red-shouldered Hawk (Buteo lineatus). In Birds of the World (1.0th ed.). Cornell Lab of Ornithology.
Ferguson-Lees, J., & Christie, D. A. (2001). Raptors of the world. Houghton Mifflin Harcourt.
Gehlbach, F. R. (2009). The eastern screech owl: Life history, ecology, and behavior in the suburbs and countryside. Texas A&M University Press.
Grigg, N. P., Krilow, J. M., Gutierrez-Ibanez, C., Wylie, D. R., Graves, G. R., & Iwaniuk, A. N. (2017). Anatomical evidence for scent guided foraging in the Turkey vulture. Scientific Reports, 7(1). https://doi.org/10.1038/s41598-017-17794-0
Kerlinger, P. (1989). Flight strategies of migrating hawks.
Kirk, D. A., Mossman, M. J., Bildstein, K. L., Naveda-Rodríguez, A., & Mallon, J. M. (2024). Turkey Vulture (Cathartes aura). In Birds of the World (2.0th ed.). Cornell Lab of Ornithology.
Lingham-Soliar, T. (2014). Feather structure, biomechanics and biomimetics: The incredible lightness of being. Journal of Ornithology, 155(2), 323-336. https://doi.org/10.1007/s10336-013-1038-0
Marti, C. D., Poole, A. F., Bevier, L. R., Bruce, M. D., Christie, D., Kirwan, G. M., Marks, J. S., & Pyle, P. (2024). American Barn Owl (Tyto furcata). In Birds of the World (1.1st ed.). Cornell Lab of Ornithology.
Odum, E. P., & Barrett, G. W. (2005). Fundamentals of ecology. Cengage Learning.
Parker, J. W. (2020). Mississippi Kite (Ictinia mississippiensis). In Birds of the World (1.0th ed.). Cornell Lab of Ornithology.
Payne, R. S. (1971). Acoustic location of prey by barn owls (Tyto Alba). Journal of Experimental Biology, 54(3), 535-573. https://doi.org/10.1242/jeb.54.3.535
Poole, A. F. (1989). Ospreys: A natural and unnatural history. Cambridge University Press.
Preston, C. R., & Beane, R. D. (2024). Red-tailed Hawk (Buteo jamaicensis). In Birds of the World (1.0th ed.). Cornell Lab of Ornithology.
Ritchison, G., Gehlbach, F. R., & Patten, M. A. (2020). Eastern Screech-Owl (Megascops asio). In Birds of the World (1.0th ed.). Cornell Lab of Ornithology.
Rosenfield, R. N., Madden, K. K., Bielefeldt, J., & Curtis, O. E. (2025). Cooper’s Hawk (Accipiter cooperii). In Birds of the World (1.2nd ed.). Cornell Lab of Ornithology.
Sarasola, J. H., Grande, J. M., & Negro, J. J. (2018). Birds of prey: Biology and conservation in the XXI century. Springer.
Verheyden, C., & Jouventin, P. (1994). Olfactory behavior of foraging Procellariiforms. The Auk, 111(2), 285-291. https://doi.org/10.2307/4088593
Ward, A. B., Weigl, P. D., & Conroy, R. M. (2002). Functional morphology of raptor Hindlimbs: Implications for resource partitioning. The Auk, 119(4), 1052-1063. https://doi.org/10.1093/auk/119.4.1052
Watson, W. A., Hofstadter, D. F., Jones, G. M., Kramer, H. A., Kryshak, N. F., Zulla, C. J.,
Whitmore, S. A., O’Rourke, V., Keane, J. J., Gutiérrez, R. J., & Peery, M. Z. (2023). Characterizing juvenile dispersal dynamics of invasive barred owls: Implications for management. Ornithological Applications, 126(1). https://doi.org/10.1093/ornithapp/duad061
Most changes in the ocean happen long before we notice them.
The water still looks blue. Waves continue to break across the sandbars. Beachgoers spread their towels beneath the same summer sun, children chase ghost crabs along the tide line, and anglers cast into the surf hoping for a bite.
Yet beneath the surface, a warming ocean is altering the conditions that shape life along the coast.
The changes begin with microscopic organisms drifting through the water column and ripple outward through fish, shellfish, jellyfish, and eventually the people who swim, fish, and play in these waters. Scientists have documented rising ocean temperatures worldwide, with the ocean absorbing the vast majority of the excess heat generated by a warming climate (IPCC, 2023; NASA, 2025).
For beachgoers along the Onslow County coast, these changes often appear as small observations. Water that feels warmer than it once did. Green swirls visible in drone photographs. Jellyfish gathering along the shoreline. Questions about bacteria, shellfish closures, and changing fish patterns.
At first glance, these may seem unrelated.
In reality, they are all connected.
A Longer Summer Beneath the Surface
The ocean does not warm as quickly as the air above it, but it holds heat much longer.
As coastal waters warm earlier in spring and remain warm later into autumn, marine organisms experience something similar to a longer growing season on land. Processes that once occurred over a few summer months may now persist for much longer periods – lasting later into the year or shifting the timing of organisms that are responding to environmental conditions (IPCC, 2023; Menzel et al., 2006).
For marine life, temperature influences nearly everything. Growth rates, feeding behavior, reproduction, migration, and metabolism are all affected by the warmth of the surrounding water (Pörtner & Knust, 2007).
For many species, warmer water means increased biological activity. But every response carries consequences that ripple through the food web.
The first organisms to respond are often the smallest.
When Tiny Things Respond First
Most beachgoers never think about what is suspended in the water around them.
Unlike a forest, marsh, or coral reef, much of the ocean’s life is not immediately visible. Looking across the surf, the water may appear empty except for an occasional fish, jellyfish, or diving bird.
Yet the water column itself is home to countless drifting organisms. Some are microscopic plants. Others are microscopic animals. Together, they form a community known as plankton.
Among the most important are phytoplankton—tiny plant-like organisms that drift with currents and tides. Though nearly invisible to the naked eye, they capture sunlight, form the foundation of marine food webs, and produce much of the oxygen found in Earth’s atmosphere (Falkowski et al., 1998).
Feeding on them are zooplankton, a diverse group of drifting animals that includes tiny crustaceans, larval fish, and the early life stages of many marine organisms. Nearly everything in the ocean depends on this microscopic world in some way.
As temperatures rise and sunlight remains abundant, phytoplankton growth can increase. In many cases, this increased productivity benefits marine ecosystems by providing more food for zooplankton, shellfish, and small fish.
Sometimes, however, the changes become visible.
Drone photographs, fishing reports, and satellite imagery occasionally reveal ribbons and swirls of green water along the coastline. Many people assume these colors indicate pollution, but the explanation is often more complex.
In some cases, the green color reflects increased concentrations of phytoplankton. In others, it may result from suspended sediment, river discharge, or other naturally occurring materials in the water (Behrenfeld et al., 2006).
Green water does not automatically mean unhealthy water.
More often, it is a visible reminder that biological activity is taking place beneath the surface—activity that most beachgoers never see.
In fact, many periods of greener water reflect productive conditions that support marine food webs. Increased phytoplankton can provide more food for zooplankton, shellfish, and small fish, creating benefits that ripple through the ecosystem. The presence of abundant microscopic life is often a sign that the ocean is actively supporting the organisms that depend upon it.
Not all blooms are beneficial, however.
Occasionally, beachgoers hear news reports about harmful algal blooms and wonder whether the water they are seeing is part of one.
Under certain conditions, a small number of phytoplankton species can reproduce so rapidly that they begin affecting the ecosystem around them. These events are known as harmful algal blooms.
Along U.S. coastlines, some of the better-known examples include Karenia brevis, which causes many Gulf Coast red tides; Alexandrium species, which can produce toxins associated with paralytic shellfish poisoning; and Pseudo-nitzschia, which produces domoic acid and has been linked to shellfish closures and wildlife impacts in several regions (Anderson et al., 2012; Trainer et al., 2012).
Unlike the seasonal increases in phytoplankton that help support marine food webs, harmful blooms can stress marine life and create concerns for people. Some produce toxins that accumulate in shellfish, leading to temporary harvesting closures. Others contribute to oxygen declines as large concentrations of algae die and decompose (Anderson et al., 2002).
For beachgoers, the challenge is that harmful blooms do not always look the way people expect. A bloom may appear as a patch of unusually dense water, a streak of discoloration, or sometimes little different from surrounding water. Color alone rarely tells the whole story.
In some cases, blooms may discolor the water, turning it red, rust-colored, brown, orange, or an unusually dense green. Some may also produce odors that people describe as sulfur-like, fishy, or similar to decaying vegetation (Gilbert et al., 2005; Gobler, 2020).
Not all green water is the same. Satellite imagery can reveal differences in phytoplankton concentrations across coastal waters. Many blooms support productive marine ecosystems, while others may become dense enough to affect water quality and ecosystem health. | Image credit: EPA cyanWeb, https://qed.epa.gov/cyanweb/
Fortunately, most periods of pale green, emerald green, or slightly tea-colored water along the Carolina coast are not harmful algal blooms. More often, they reflect normal concentrations of phytoplankton, suspended sediment, river discharge, or other natural processes.
The challenge is that the water does not always reveal which is which at first glance. What appears to be a simple color change may be telling a much more complicated story beneath the surface.
The Oxygen Paradox
Warm water creates a biological contradiction.
As temperatures rise, marine organisms require more oxygen to stay active and carry out basic life processes. At the same time, warmer water naturally holds less dissolved oxygen—the tiny oxygen molecules mixed into the water that fish, crabs, and many other marine animals breathe. Unlike oxygen in the air around us, this oxygen must remain suspended within the water itself, and warmer water cannot hold as much of it as cooler water (Keeling et al., 2010).
In other words, as the demand for oxygen increases, the supply decreases. Scientists refer to this growing challenge as ocean deoxygenation, a phenomenon driven in part by warming oceans and documented in coastal waters around the world (Breitburg et al., 2018; Diaz & Rosenberg, 2008).
The effects are often invisible to beachgoers. Unlike a jellyfish bloom or a patch of green water, low oxygen leaves few obvious clues for someone standing on the shoreline.
Fish may become sluggish, gather near inlets or channels, or disappear from places where they are normally common long before any obvious signs appear at the surface. Crabs, shrimp, and other marine organisms must work harder to find places with enough oxygen to survive. Some may move into shallower water, concentrate in tidal channels, or bury themselves in sediment where conditions remain tolerable. Some areas become less favorable, while others provide temporary pockets of suitable habitat.
The ocean begins to rearrange itself.
Following the Fish
Stand on the beach long enough and patterns begin to emerge.
A stretch of water that looked empty an hour ago suddenly flickers with baitfish. Birds gather over a patch of surf. A school of fish appears just beyond a sandbar, then vanishes as quickly as it arrived.
Most of these movements happen without drawing much attention. To someone walking the shoreline, the ocean can seem unchanged from one day to the next.
Beneath the surface, however, marine life is constantly adjusting.
Fish are not fixed to one place. They move through the water searching for conditions that suit them, often responding to changes that people cannot see. A slight difference in temperature, a pocket of water with more oxygen, or a concentration of prey can be enough to shift where fish gather (Pörtner & Knust, 2007).
Along the beaches of Onslow County, these adjustments may be playing out right in front of us.
Anglers sometimes notice schools of mullet, menhaden, silversides, or other baitfish stacked along a sandbar. Predatory fish such as bluefish, Spanish mackerel, red drum, or even small sharks may linger near an inlet. Feeding activity may suddenly erupt close to shore, with baitfish leaping from the water as predators chase them, birds diving repeatedly into the surf, and flashes of silver visible just beyond the breakers. Tides, currents, and seasonal migrations all help shape these patterns, but fish are also responding to the changing conditions around them.
Even the breaking surf can matter.
Where waves tumble across shallow bars, the water is constantly being mixed and stirred. Oxygen from the atmosphere is worked back into the water, creating conditions with higher oxygen levels than nearby areas where the water is calmer and moves less. What looks like nothing more than a line of breaking waves can become a place where marine life gathers.
Most beachgoers never notice these subtle shifts.
They simply see fish where fish happen to be.
Yet changing ocean conditions are becoming an increasingly important part of the story. Fish may feed in a different stretch of surf than usual, baitfish may gather in unexpected places, or seasonal arrivals may occur a little earlier or later than expected. Most of the time, the reasons remain hidden beneath the surface, but the movements themselves reveal that marine life is responding to a changing ocean (Pinsky et al., 2013).
The ocean is not standing still.
And neither are the fish.
The Species That Thrive
Not every organism responds to warming water in the same way.
Some struggle.
Others thrive.
For many beachgoers, one of the most noticeable signs of seasonal change arrives as translucent shapes drifting through the surf. As plankton populations increase and warm conditions persist, the same environmental changes influencing fish and other marine life can also create favorable conditions for jellyfish.
Jellyfish are a familiar part of coastal life in Onslow County, but their numbers can vary dramatically from season to season. During late spring, summer, and early fall, when air and water temperatures commonly reach about 68–86°F (20–30°C), conditions often become more favorable for larger jellyfish populations than during the colder months.
Most people first notice them while wading in the shallows, scanning the water from a pier, or walking the beach after a storm. A shoreline that seemed empty a few weeks earlier may suddenly hold dozens of stranded jellyfish along the tide line. Depending on the season, visitors might encounter moon jellies pulsing just beneath the surface, cannonball jellies washing ashore in clusters, or the unmistakable blue floats of Portuguese man o’ war carried in by winds and currents.
A shoreline covered with cannonball jellies can appear almost overnight. In reality, the conditions supporting these blooms often develop over weeks or months as water temperatures, food availability, and ocean currents change. | Image credit: Cape Hatteras National Seashore
These appearances can feel sudden, but they rarely are.
A shoreline that seems free of jellyfish one week may be dotted with them the next. To someone standing on the beach, it can feel as though they arrived overnight.
Much of a jellyfish’s life unfolds out of sight. Many drift offshore, while others pass through life stages that most people never notice. As waters warm and food becomes more abundant, conditions can support larger populations. Sometimes the result is a bloom—a period when unusually large numbers gather in coastal waters and become difficult to ignore.
In reality, the conditions that support them may have been developing for weeks or even months. While warmer water does not automatically mean more jellyfish everywhere (Condon et al., 2012), seasonal warming can contribute to periods when jellyfish become unusually abundant in nearshore waters. Currents, food availability, and other environmental factors also influence when and where these blooms occur (Purcell, 2005; Richardson et al., 2009).
For observers on the shore, jellyfish are often among the first visible reminders that changes in ocean conditions do not stay hidden beneath the surface for long.
Not every organism has the ability to drift or swim away.
The Organisms That Cannot Leave
Fish can relocate.
Jellyfish can drift with currents.
Shellfish remain where they are.
For many beachgoers, oysters, clams, and mussels are simply part of the coastal landscape—something encountered at low tide, served at a seafood restaurant, or harvested during shellfish season.
Yet these animals spend their lives doing something remarkable.
Oysters, clams, mussels, and other shellfish continuously draw water through their bodies, removing microscopic food particles as they feed. This is why they are known as filter feeders. A single adult oyster can filter up to 50 gallons (190 L) of water per day, depending on temperature, salinity, and other environmental factors (Jansen, 2023; zu Ermgassen et al., 2012).
An oyster reef does not simply sit on the bottom. Day and night, every oyster is quietly filtering the estuary around it.
Because they process so much water, shellfish become closely connected to the conditions around them. Changes in temperature, oxygen levels, harmful algal blooms, and water quality can all affect their health and survival (Shumway, 1990).
For this reason, shellfish often serve as some of the earliest indicators that environmental conditions have changed.
When shellfish harvesting areas are temporarily closed, many people assume pollution is the only explanation. In reality, closures may occur for a variety of reasons, including elevated levels of bacteria such as fecal coliforms, Escherichia coli (E. coli), or Enterococcus, harmful algal blooms, or other conditions that could affect human health (Food & Drug Administration (FDA), 2023).
In many cases, these closures are evidence that monitoring programs are working exactly as intended.
The shellfish are not causing the problem.
They are revealing it.
By filtering the surrounding water day after day, they provide a glimpse into conditions that might otherwise go unnoticed.
Sometimes, what they reveal is a bacterium that has received increasing attention in recent years.
The Bacteria That Was Already Here
Few marine organisms have generated more public concern in recent summers than Vibrio bacteria.
News headlines often make it sound like a new arrival.
It is not.
Like the phytoplankton, zooplankton, and countless other organisms drifting through coastal waters, Vibrio vulnificushas always been part of the hidden community beneath the surface.
Most beachgoers never notice it. They cannot see it. They do not think about it while wading through the surf or collecting shells along the shoreline.
Yet these bacteria have long occupied an important ecological role.
Vibrio species occur naturally in coastal and estuarine waters around the world. They help break down organic matter and recycle nutrients, returning materials to the food web where they can be used again by other organisms. If they were somehow eradicated, scientists would expect dead plants, algae, fish, and other organic material to break down more slowly. Over time, beach wrack could linger longer along shorelines, decaying material could accumulate in marshes and tidal flats, and nutrients normally returned to the water and sediment would become less available to the organisms that depend on them. These changes might not be obvious at first, but they could gradually alter the health and productivity of coastal ecosystems (Oliver, 2005).
The organic material accumulating along a wrack line supports a hidden community of decomposers. Among them are naturally occurring bacteria that help recycle nutrients and keep coastal ecosystems functioning. Image credit: S. Hilldebrand, U. S. Fish and Wildlife Service
What often changes first is not the presence of these organisms, but their abundance.
Just as warmer conditions can influence phytoplankton growth, they can also affect microbial communities.
Most of the time, these changes remain invisible.
The water may look the same. The beach may feel the same. Nothing about a morning walk along the shoreline suggests that microscopic populations are shifting beneath the surface.
Yet they are.
When water temperatures rise well above the normal seasonal range for a region and remain elevated for extended periods, conditions can become more favorable for certain Vibrio species. Their populations may increase, raising the likelihood of human exposure (Baker-Austin et al., 2012; Baker-Austin et al., 2018).
For most healthy beachgoers, swimming in coastal waters remains a normal part of enjoying the beach.
However, individuals with open wounds, compromised immune systems, or underlying health conditions may face greater risks and should pay closer attention to local advisories and public health guidance.
The story is not really about a dangerous bacterium suddenly appearing where it did not belong.
It is another example of a broader pattern that runs throughout coastal ecosystems.
As environmental conditions change, the organisms already living there respond. Some become more abundant. Others become less common. Together, their responses reveal something easy to miss while standing at the water’s edge: the shoreline is alive with countless forms of life that most of us never see.
Even the smallest inhabitants are connected to the larger changes unfolding around them.
Reading the Signs
Most beachgoers will never measure dissolved oxygen or monitor water temperatures.
What they will notice are the signs: water that stays warm later into autumn, green swirls visible from a fishing pier or drone photograph, jellyfish gathering along a tide line, fish appearing in unexpected places, temporary shellfish closures, or questions about bacteria that have long existed in coastal waters.
None of these observations tells the whole story on its own.
Taken together, however, they reveal an ecosystem responding to warmer conditions one species, one season, and one degree at a time.
Looking Beneath the Surface
Most changes in the ocean begin out of sight.
Long before beachgoers notice a jellyfish drifting through the surf or a patch of green water offshore, microscopic organisms are already responding to changing conditions. Fish adjust their movements. Oxygen levels shift. Shellfish filter whatever the water brings.
By the time we notice the signs, the ecosystem has often been responding for weeks or months.
The water may feel the same as it always has beneath our feet. Yet each summer offers new clues about the changes taking place below the surface—if we know where to look.
The ocean often appears unchanged from one day to the next. Beneath the surface, however, countless organisms are responding to shifting temperatures, oxygen levels, food availability, and water quality. The more we learn to observe, the more the shoreline reveals. | Image credit: A. Mitchell
References
Anderson, D. M., Cembella, A. D., & Hallegraeff, G. M. (2012). Progress in understanding harmful algal blooms: Paradigm shifts and new technologies for research, monitoring, and management. Annual Review of Marine Science, 4(1), 143-176. https://doi.org/10.1146/annurev-marine-120308-081121
Anderson, D. M., Glibert, P. M., & Burkholder, J. M. (2002). Harmful algal blooms and eutrophication: Nutrient sources, composition, and consequences. Estuaries, 25(4), 704-726. https://doi.org/10.1007/bf02804901
Baker-Austin, C., Oliver, J. D., Alam, M., Ali, A., Waldor, M. K., Qadri, F., & Martinez-Urtaza, J. (2018). Vibrio spp. infections. Nature Reviews Disease Primers, 4(1), 1-9. https://www.nature.com/articles/s41572-018-0005-8
Baker-Austin, C., Trinanes, J. A., Taylor, N. G., Hartnell, R., Siitonen, A., & Martinez-Urtaza, J. (2012). Emerging vibrio risk at high latitudes in response to ocean warming. Nature Climate Change, 3(1), 73-77. https://doi.org/10.1038/nclimate1628
Behrenfeld, M. J., O’Malley, R. T., Siegel, D. A., McClain, C. R., Sarmiento, J. L., Feldman, G. C., Milligan, A. J., Falkowski, P. G., Letelier, R. M., & Boss, E. S. (2006). Climate-driven trends in contemporary ocean productivity. Nature, 444(7120), 752-755. https://doi.org/10.1038/nature05317
Breitberg, D., Levin, L. A., Oschlies, A., Grégoire, M., Chavez, F. P., Conley, D. J., Garçon, V., Gilbert, D., Gutiérrez, D., & Zhang, J. (2018). Declining oxygen in the global ocean and coastal waters. Science, 359(6371). https://doi.org/10.1126/science.aam7240
Condon, R. H., Graham, W. M., Duarte, C. M., Pitt, K. A., Lucas, C. H., Haddock, S. H., Sutherland, K. R., Robinson, K. L., Dawson, M. N., Decker, M. B., Mills, C. E., Purcell, J. E., Malej, A., Mianzan, H., Uye, S., Gelcich, S., & Madin, L. P. (2012). Questioning the rise of gelatinous zooplankton in the world’s oceans. BioScience, 62(2), 160-169. https://doi.org/10.1525/bio.2012.62.2.9
Diaz, R. J., & Rosenberg, R. (2008). Spreading dead zones and consequences for marine ecosystems. Science, 321(5891), 926-929. https://doi.org/10.1126/science.1156401
Falkowski, P. G., Barber, R. T., & Smetacek, V. (1998). Biogeochemical controls and feedbacks on ocean primary production. Science, 281(5374), 200-206. https://doi.org/10.1126/science.281.5374.200
Food & Drug Administration (FDA). (2023). National Shellfish Sanitation Program (NSSP) Guide for the Control of Molluscan Shellfish (2023 Revision). U. S. Food and Drug Administration. https://www.fda.gov/media/181370/download?attachment
Glibert, P., Anderson, D., Gentien, P., Granéli, E., & Sellner, K. (2005). The global, complex phenomena of harmful algal blooms. Oceanography, 18(2), 136-147. https://doi.org/10.5670/oceanog.2005.49
IPCC. (2023). Climate change 2023: Synthesis report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change (IPCC). https://doi.org/10.59327/IPCC/AR6-9789291691647
Menzel, A., Sparks, T. H., Estrella, N., Koch, E., Aasa, A., Ahas, R., Alm-Kübler, K., Bissolli, P., Braslavská, O., Breide, A., Chmielewski, F. M., Crepinsek, Z., Curnel, Y., Dahl, Å., Defila, C., Donnelly, A., Filella, Y., Jatczak, K., Måge, F., … Zust, A. (2006). European phenological response to climate change matches the warming pattern. Global Change Biology, 12(10), 1969-1976. https://doi.org/10.1111/j.1365-2486.2006.01193.x
Oliver, J. D. (2005). Wound infections caused by Vibrio vulnificus and other marine bacteria. Epidemiology and Infection, 133(3), 383-391. https://doi.org/10.1017/s0950268805003894
Pinsky, M. L., Worm, B., Fogarty, M. J., Sarmiento, J. L., & Levin, S. A. (2013). Marine taxa track local climate velocities. Science, 341(6151), 1239-1242. https://doi.org/10.1126/science.1239352
Pörtner, H. O., & Knust, R. (2007). Climate change affects marine fishes through the oxygen limitation of thermal tolerance. Science, 315(5808), 95-97. https://doi.org/10.1126/science.1135471
Purcell, J. E. (2005). Climate effects on formation of jellyfish and ctenophore blooms: A review. Journal of the Marine Biological Association of the United Kingdom, 85(3), 461-476. https://doi.org/10.1017/s0025315405011409
Richardson, A. J., Bakun, A., Hays, G. C., & Gibbons, M. J. (2009). The jellyfish joyride: Causes, consequences and management responses to a more gelatinous future. Trends in Ecology & Evolution, 24(6), 312-322. https://doi.org/10.1016/j.tree.2009.01.010
Shumway, S. E. (1990). A review of the effects of algal blooms on shellfish and aquaculture. Journal of the World Aquaculture Society, 21(2), 65-104. https://doi.org/10.1111/j.1749-7345.1990.tb00529.x
Trainer, V. L., Bates, S. S., Lundholm, N., Thessen, A. E., Cochlan, W. P., Adams, N. G., & Trick, C. G. (2012). Pseudo-nitzschia physiological ecology, phylogeny, toxicity, monitoring and impacts on ecosystem health. Harmful Algae, 14, 271-300. https://doi.org/10.1016/j.hal.2011.10.025
Zu Ermgassen, P. S., Spalding, M. D., Grizzle, R. E., & Brumbaugh, R. D. (2012). Quantifying the loss of a marine ecosystem service: Filtration by the eastern oyster in US estuaries. Estuaries and Coasts, 36(1), 36-43. https://doi.org/10.1007/s12237-012-9559-y
Most beachgoers look across the shoreline and see a boundary.
The ocean ends. The land begins.
But the strip of sand where waves wash ashore and slide back toward the sea is not really either one. It is a threshold—a place that becomes ocean and land again with every passing wave.
At first glance, this narrow band of wet sand appears empty. There are no marsh grasses, no oyster reefs, and no obvious schools of fish. Yet beneath the surface, the sand is alive with animals digging, filtering, feeding, hunting, and breathing.
This is the swash zone: the constantly shifting seam between ocean and land.
It is one of the most overlooked ecosystems on the North Carolina coast.
The swash zone is the narrow strip of shoreline where waves wash ashore and then retreat back toward the sea. Though it may appear to be little more than wet sand, it supports a diverse community of animals adapted to life between ocean and land. | Image credit: J. Morales
The Beach That Never Stops Moving
Unlike a marsh, oyster reef, or seagrass meadow, the swash zone never stays still.
Each wave pushes seawater into the sand and then pulls it back out again. Water moves through the spaces between sand grains, carrying oxygen, microscopic algae, bacteria, and organic matter. The sand itself acts almost like a living filter, supporting communities of organisms adapted to conditions that change minute by minute (Brown & McLachlan, 2018; McLachlan & Defeo, 2018).
To survive here, animals must tolerate burial, shifting sediments, crashing waves, changing salinity, and predators arriving from both land and sea.
Few species can endure such instability.
Those that do are specialists (Defeo et al., 2009).
The Living Wave Riders: Mole Crabs and Coquina Clams
If you’ve ever noticed the wet sand suddenly shimmer or seem to move as a wave retreats, you’ve likely witnessed two of the swash zone’s most abundant residents.
Atlantic Mole Crabs (Emerita talpoida)
An Atlantic mole crab, in Surf City, NC, briefly exposed at the surface of the swash zone. Within seconds, these specialized crustaceans can bury themselves beneath the sand, where they spend most of their lives filtering food from the surf. | Image credit: johnnybirder, iNaturalist
Known locally as sand fleas, Atlantic mole crabs spend nearly their entire lives buried beneath the surface of the swash zone.
They are not true crabs. Instead, they belong to a group of highly specialized crustaceans adapted for life where waves break on the shore. Their bodies are smooth, streamlined, and shaped almost like a small bean. Using powerful rear legs, they can bury themselves in saturated sand in seconds (Abude et al., 2024).
When waves wash overhead, they extend feathery antennae into the water and filter microscopic plankton and organic particles from the surf (Abude et al., 2024).
Rather than remaining stationary, mole crabs occupy the constantly shifting swash zone, where food and oxygen are delivered by breaking waves. Their abundance makes them one of the most important food sources for shorebirds, fish, and ghost crabs (Abude et al., 2024).
Coquina Clams (Donax variabilis)
Sharing the same habitat is one of the most recognizable shells on Atlantic beaches.
Coquina clams are the tiny, brightly colored shells scattered across the tide line in shades of pink, yellow, purple, blue, orange, and white.
Most people only notice the shells.
The living animal beneath them is remarkably adapted to life in moving sand.
Coquinas live just beneath the surface of the swash zone where they filter microscopic algae and suspended particles from the water. As waves advance and retreat, they repeatedly rebury themselves, using a muscular foot to dig into the sand with astonishing speed (Ellers, 1995).
Like mole crabs, coquinas are adapted to the dynamic conditions of the swash zone. Their abundance provides food for fish, crabs, and shorebirds, making them a critical link between microscopic plankton and larger coastal predators (Wilson, 1999).
Standing at the water’s edge, it is easy to think the beach is motionless.
In reality, thousands of coquinas and mole crabs may be moving beneath your feet with every wave.
The Night Shift: Atlantic Ghost Crabs (Ocypode quadrata)
Higher on the beach, above the reach of most waves, another resident waits.
Atlantic ghost crabs spend daylight hours hidden inside deep burrows excavated into the sand. Their pale coloration blends almost perfectly with the beach, making them difficult to see unless they move.
Atlantic ghost crabs spend daylight hours hidden in burrows above the tide line. Their pale coloration provides excellent camouflage against the sand, making them surprisingly difficult to spot until they move. | Image credit: A. Mitchell
While the swash zone below is dominated by animals filtering food from the surf, ghost crabs are hunters and scavengers.
After sunset, they emerge to patrol the shoreline, feeding on mole crabs, coquina clams, stranded marine organisms, insects, carrion, and whatever other opportunities the beach provides (Wolcott, 1978).
Many beachgoers never see them at all. Instead, they notice the evidence they leave behind. Round burrow openings dot the upper beach. Fresh tracks crisscross the sand overnight and disappear with the next tide. Occasionally, a pale shape darts sideways through the beam of a flashlight before vanishing into darkness.
Those burrows tell a story of their own. Beaches with abundant ghost crab burrows often support richer communities of animals living both above and below the sand, which is why scientists sometimes use ghost crabs as one way of assessing beach condition and disturbance (Schlacher et al., 2016).
The next time you notice a round hole in the upper beach with a pile of freshly excavated sand nearby, you are likely looking at the entrance to a ghost crab burrow—and evidence that the beach is still very much alive after dark.
Between the Grains
The largest residents of the swash zone are only part of the story.
Beneath the surface lies an even larger community that most beachgoers never see. Between individual grains of sand are tiny water-filled spaces that form a hidden habitat known as the interstitial zone. To us, a handful of wet sand looks solid. To these organisms, it is an underwater landscape of tunnels, chambers, and passageways (Higgins & Thiel, 1988).
The beach is layered with hidden communities. From amphipods and ghost crabs higher on the shore to coquina clams and mole crabs at the water’s edge, different species occupy distinct zones shaped by waves, moisture, food availability, and shifting sand. | Image credit: Michel et al., 2016
Amphipods: The Cleanup Crew
The line of seaweed, shells, and debris left behind by the tide may look messy, but it is often one of the busiest places on the beach.
Hidden among the wrack, in the upper intertidal zone, are amphipods, small crustaceans often called Atlantic beach hoppers (Americorchestia longicornis). If you sift through a pile of damp seaweed or drift algae, you may catch a glimpse of them springing away before disappearing back into cover.
Much of what washes ashore eventually becomes food for something else. Amphipods feed on decaying seaweed, dead animals, and other organic material stranded by the tide. In doing so, they help break down material that would otherwise accumulate along the shoreline. They also become food themselves, supporting shorebirds, fish, and other invertebrates that forage along the beach (Dugan et al., 2003).
Polychaete Worms: Engineers Beneath the Sand
Most beachgoers never see the worms living beneath the tide line, but their work is happening constantly beneath the surface.
As polychaete worms burrow through the sand, they create tiny pathways that allow water and oxygen to penetrate deeper into the sediment. In many ways, they perform the same role that earthworms do in a garden, except their garden is the beach itself.
Some species spend their lives feeding on organic material trapped between the sand grains, such as Lugworms (Arenicolidae). Others hunt small crustaceans and worms moving through the sediment such as Bloodworms (Glyceridae) and Paddle Worms / Shimmy Worms (Nephtyidae). As they burrow, feed, and move through the beach, they continually mix the sand and help create conditions that allow countless other organisms to survive there (McLachlan & Defeo, 2018).
Ribbon Worms: Hidden Predators
Not every animal beneath the sand is feeding on algae, bacteria, or decaying material.
Ribbon worms (Nemertea) are predators, though few people ever realize they are there. Hidden beneath the surface, they hunt some of the same tiny animals that share the spaces between the sand grains, including small worms, crustaceans, and other invertebrates moving through the sediment (Thiel & Kruse, 2001).
Many possess a remarkable feeding structure called a proboscis that can be rapidly extended to capture prey (Thiel & Kruse, 2001).
Most beachgoers will never see a ribbon worm, yet they are part of the same hidden food web as the amphipods, copepods, and nematodes surrounding them. Even beneath a seemingly empty stretch of sand, animals are feeding, avoiding predators, and competing for resources every hour of the day.
Nematodes: Life at Microscopic Scale
If you could shrink yourself down and explore a handful of wet sand, the landscape would look very different.
What appears solid to us is actually filled with tiny spaces between the grains. Moving through those water-filled passages are microscopic animals called nematodes (phylum Nematoda).
These tiny roundworms feed on bacteria, algae, fungi, and organic matter coating the sand. Though nearly invisible, they are among the most abundant animals on many beaches and play an important role in breaking down organic material and recycling nutrients throughout the sediment (Coull, 1999; Schratzberger & Ingels, 2018).
Harpacticoid Copepods: Tiny Links in the Food Web
Sharing those same microscopic spaces are harpacticoid copepods (Paraleptastacus wilsoni), tiny crustaceans that spend their lives moving between individual sand grains.
They graze on algae and microbial films coating the sediment, feeding on resources too small for larger animals to use directly. In turn, they become prey for larger invertebrates and juvenile fishes.
Most beachgoers will never see a harpacticoid copepod. Yet every handful of wet sand may contain a community of animals like these, quietly connecting the microscopic world to the larger food web of the beach (Schratzberger & Ingels, 2018).
Individually, these animals are easy to overlook.
Collectively, they form much of the living foundation of the tide line. The coquinas, mole crabs, ghost crabs, fishes, and shorebirds visible along the shoreline all depend, directly or indirectly, on countless small interactions taking place beneath the sand.
Following the Birds
One of the easiest ways to observe this hidden ecosystem is not by looking down.
It is by looking up.Anyone who spends time on the beach has likely watched sanderlings (Calidris alba) racing along the edge of the surf. They dart forward as a wave retreats, stop suddenly to probe the sand, and then sprint away from the next incoming wave. A little farther up the beach, ruddy turnstones (Arenaria interpres) pick through wrack lines left behind by the tide. Along the surf edge, Eastern willets (Tringa semipalmata semipalmata) walk deliberately through the shallows, searching for movement beneath the water.
To many beachgoers, they are simply birds feeding along the shoreline.
What they are actually doing is reading the beach.
Each probe into the sand is a search for prey hidden beneath the surface. Mole crabs, small worms, amphipods, coquinas, and other invertebrates living within the tide line provide food for these birds (Dugan et al., 2003; Hubbard & Dugan, 2003).
The birds go where the food is.
When shorebirds gather along a stretch of beach, they are often revealing an ecosystem that would otherwise remain invisible. Their presence tells us that the sand beneath them is alive with prey, even if we cannot see it ourselves.
In many ways, shorebirds act as interpreters of the tide line. By watching where they feed, pause, and congregate, we gain a glimpse into the hidden community supporting them below.
Reading the Beach
From a distance, the tide line can seem almost empty. A narrow strip of wet sand separates the ocean from the rest of the beach. Waves arrive, waves leave, and little appears to change.
Spend a few minutes watching, however, and a different picture begins to emerge.
Shorebirds gather where the surf is most active. Tiny shells appear and disappear with the retreating waves. Fresh ghost crab burrows punctuate the upper beach. Even the wrack line left behind by the tide becomes a gathering place for scavengers and foraging birds.
What first appears to be a simple boundary between land and sea begins to look more like a busy shoreline neighborhood.
At first glance, the tide line can appear almost empty. Look a little longer, however, and the clues begin to emerge—feeding shorebirds, scattered shells, and the constant movement of the surf all hint at the hidden community living beneath the sand. | Image credit: A. Mitchell
The animals living here are responding to the same thing: the constant movement of the tide. Food arrives with the surf, becomes available for a brief moment, and is quickly claimed by whatever creature is best adapted to find it. Some filter it from the water. Some collect it from the sand. Others hunt the animals already feeding there.
Because these organisms live so closely tied to the conditions of the beach, changes in their numbers can provide clues about the habitat itself (Defeo et al., 2009). A shoreline where birds are feeding, ghost crab burrows remain active, and life continues to reveal itself at the edge of the surf is often a sign that this narrow strip of beach is supporting the community that depends upon it.
When those communities decline, the change may not be immediately obvious. Yet over time the beach can begin to feel quieter. Fewer birds stop to feed. Fewer burrows appear in the sand. The signs become harder to find. Those changes can ripple outward through the food web, affecting species both on the beach and beyond it (Peterson et al., 2006).
The Threshold
The next time you stand at the edge of the surf, watch where the waves pause before sliding back toward the sea.
It is easy to see this narrow strip of shoreline as a boundary. Ocean on one side. Land on the other.
But the tide line is not really a dividing line at all.
It is a place where both worlds meet.
With every passing wave, food, oxygen, and life arrive from the ocean. Beneath the sand, animals capture it, consume it, recycle it, and pass it on. Shorebirds search for it. Ghost crabs emerge after dark to hunt it. Countless organisms spend their entire lives within a space that is neither fully ocean nor fully land.
Most people walk across this strip of beach without ever noticing it.
Yet it is one of the busiest places along the coast.
The next time you see shells appearing and disappearing in the surf, a flock of sanderlings racing the tide, or ghost crab burrows scattered across the upper beach, remember that these are not separate observations. They are pieces of the same story.
What appears to be an empty stretch of wet sand is actually a living threshold—a place where ocean and land remain connected through countless interactions happening beneath every step.
And once you see it, it becomes difficult to look at the shoreline the same way again.
The tide line in Surf City, NC may appear to be little more than wet sand. Yet beneath every retreating wave lies a hidden community connecting ocean and land through countless interactions, most of them unseen. | Image credit: A. Mitchell
References
Abude, R. R., Lôbo-Hajdu, G., Moreira, D. A., & Cabrini, T. M. (2024). Sandy beach mole crabs (Decapoda: Hippidae: Emerita): A systematic review of the anthropic impacts, populations density, and conservation strategies. Marine Environmental Research, 202, 106745. https://doi.org/10.1016/j.marenvres.2024.106745
Defeo, O., McLachlan, A., Schoeman, D. S., Schlacher, T. A., Dugan, J., Jones, A., Lastra, M., & Scapini, F. (2009). Threats to sandy beach ecosystems: A review. Estuarine, Coastal and Shelf Science, 81(1), 1-12. https://doi.org/10.1016/j.ecss.2008.09.022
Dugan, J. E., Hubbard, D. M., McCrary, M. D., & Pierson, M. O. (2003). The response of macrofauna communities and shorebirds to macrophyte wrack subsidies on exposed sandy beaches of Southern California. Estuarine, Coastal and Shelf Science, 58, 25-40. https://doi.org/10.1016/s0272-7714(03)00045-3
Ellers, O. (1995). Behavioral control of swash-riding in the clam Donax variabilis. The Biological Bulletin, 189(2), 120-127. https://doi.org/10.2307/1542462
Hubbard, D. M., & Dugan, J. E. (2003). Shorebird use of an exposed sandy beach in Southern California. Estuarine, Coastal and Shelf Science, 58, 41-54. https://doi.org/10.1016/s0272-7714(03)00048-9
McLachlan, A., & Defeo, O. (2018). The ecology of sandy shores (3rd ed.). Academic Press.
P, H. R., & Thiel, H. (1988). Intro study meiofauna. Smithsonian Books (DC).
Peterson, C. H., Bishop, M. J., Johnson, G. A., D’Anna, L. M., & Manning, L. M. (2006). Exploiting beach filling as an unaffordable experiment: Benthic intertidal impacts propagating upwards to shorebirds. Journal of Experimental Marine Biology and Ecology, 338(2), 205-221. https://doi.org/10.1016/j.jembe.2006.06.021
Pilkey, O. H., Rice, T. M., & Neal, W. J. (2014). How to read a North Carolina beach: Bubble holes, Barking sands, and rippled Runnels. UNC Press Books.
Schlacher, T. A., Lucrezi, S., Connolly, R. M., Peterson, C. H., Gilby, B. L., Maslo, B., Olds, A. D., Walker, S. J., Leon, J. X., Huijbers, C. M., Weston, M. A., Turra, A., Hyndes, G. A., Holt, R. A., & Schoeman, D. S. (2016). Human threats to sandy beaches: A meta-analysis of ghost crabs illustrates global anthropogenic impacts. Estuarine, Coastal and Shelf Science, 169, 56-73. https://doi.org/10.1016/j.ecss.2015.11.025
Schratzberger, M., & Ingels, J. (2018). Meiofauna matters: The roles of meiofauna in benthic ecosystems. Journal of Experimental Marine Biology and Ecology, 502, 12-25. https://doi.org/10.1016/j.jembe.2017.01.007
Thiel, M., & Kruse, I. (2001). Status of the nemertea as predators in marine ecosystems. Hydrobiologia, 456(1-3), 21-32. https://doi.org/10.1023/a:1013005814145
Wilson, J. G. (1999). Population dynamics and energy budget for a population of Donax variabilis (Say) on an exposed South Carolina beach. Journal of Experimental Marine Biology and Ecology, 239(1), 61-83. https://doi.org/10.1016/s0022-0981(99)00027-1
Wolcott, T. G. (1978). Ecological role of ghost crabs, Ocypode quadrata (Fabricius) on an ocean beach: Scavengers or predators? Journal of Experimental Marine Biology and Ecology, 31(1), 67-82. https://doi.org/10.1016/0022-0981(78)90137-5
Most people standing on the beach watch the Atlantic as though the ocean ends where detail disappears.
Nearshore water is easy to read. Pelicans diving offshore reveal where baitfish have gathered near the surface. The first sea turtle crawls of the season begin appearing along the upper beach. Sandbars reveal themselves through shifting wave patterns and changes in water color. Even when the water is murky, the coastline still feels structured because the movement happening near shore leaves visible clues.
Farther offshore, those visible clues become harder to read.
Beyond the breakers, past the shrimp boats and distant military vessels that sometimes mark the horizon, the Atlantic off Onslow County drops across the continental shelf into deeper pelagic water. From shore, that open water can appear empty simply because most of its structure is hidden beneath distance, depth, and moving currents. But the offshore ocean is highly organized. Temperature layers separate water masses. Squid and fish rise toward the surface at night and descend again before daylight. Currents gather plankton and compress bait schools into dense patches of life that may stretch for miles before dissolving again.
And moving through those shifting layers are sharks most beachgoers never see.
Species like the bigeye thresher shark, scalloped hammerhead, Carolina hammerhead, smooth hammerhead, great hammerhead, and tiger shark all occupy different parts of the same Atlantic system connected to North Carolina’s coast. They are not interchangeable predators simply sharing the same water. Each species is specialized for a different way of hunting, sensing, and moving through the pelagic environment.
Even though most people never see these sharks directly, their influence does not remain offshore.
They work their way back toward the coast through changes in prey behavior, bait distribution, migration timing, and the balance of the food web itself.
The Shark Built for Dim Water
The bigeye thresher shark (Alopias superciliosus) does not resemble most sharks people imagine from coastal documentaries or fishing piers. Its eyes are unusually large, and nearly half of its body length is tail.
A bigeye thresher shark (Alopias superciliosus) moves through dim offshore Atlantic water beyond the Carolina coast. Its enlarged eyes help it hunt in low light, while its elongated tail can be used to stun schooling prey before feeding. | Image credit: NC Sea Grant
Both features are tied directly to life in deeper offshore water.
Bigeye threshers spend much of their time moving vertically through the water column, often descending into dim water during daylight hours and returning closer to the surface at night as squid and mesopelagic fish migrate upward under darkness (Weng & Block, 2004). Offshore pelagic systems are layered environments. Light fades rapidly with depth, and many prey species spend daylight hours far below the surface where visibility is limited.
The shark’s large eyes help gather more available light in those darker layers.
For someone standing on the beach at sunset, the horizon still appears bright. Offshore, hundreds of feet below the surface, the bigeye thresher is already hunting in water where daylight barely penetrates.
Its tail is equally specialized. Schooling fish survive by moving together in synchronized motion, creating confusion for predators trying to isolate individual prey. The elongated upper lobe of the thresher’s tail evolved as a way to disrupt that coordination. Researchers have documented threshers using powerful overhead tail strikes to stun schooling fish before circling back to feed (Oliver et al., 2013).
That hunting strategy matters ecologically because the species targeted by threshers are often highly connected to broader Atlantic food webs. Squid, mackerel, and schooling pelagic fish move energy between offshore and coastal systems. Large predators help regulate those populations and alter how tightly schools gather, where they move, and how heavily they feed on smaller forage species beneath them in the food web (Heithaus et al., 2008).
Without predators thinning and disrupting those mid-level prey schools, feeding pressure shifts downward. Larger populations of squid and predatory fish consume more small forage species, including baitfish that later support seabirds, larger fish, and predators closer to shore. The result is not an empty ocean, but a gradual reorganization of how energy moves through the coastal ecosystem.
What beachgoers may eventually notice are changes in feeding activity: fewer concentrated bird flocks offshore, shifting bait movements, or less predictable surface eruptions beyond the breakers.
The Sharks That Hunt Electricity
Hammerheads occupy a different sensory world than most coastal predators.
The broad hammer-shaped head shared by species like the scalloped hammerhead, great hammerhead, smooth hammerhead, and Carolina hammerhead is called a cephalofoil. Spread across that wide structure are sensory pores known as ampullae of Lorenzini, specialized organs capable of detecting weak electrical fields produced by other animals (Kajiura, 2001).
Every muscle contraction and heartbeat generated by prey produces tiny electrical signals in the water.
A stingray buried beneath sand may be invisible to a human observer, but to a hammerhead it is still broadcasting electrical information.
The widened head helps the shark compare those signals across a broader sensory field, improving directional accuracy while hunting. Scientists have compared shark electroreception to detecting the output of a small household battery from extraordinary distances under ideal conditions, though in the ocean the system functions at close range to help sharks pinpoint hidden prey.
While beachgoers scan the water looking for dorsal fins, hammerheads are effectively scanning the seafloor for living electrical currents.
That sensory adaptation helps explain why multiple hammerhead species can occupy overlapping Atlantic waters without performing identical ecological roles.
The Offshore Traveler
The scalloped hammerhead (Sphyrna lewini) is one of the more oceanic hammerhead species associated with continental shelf edges, offshore structures, and migratory routes through deeper Atlantic water (Klimley, 1993).
A scalloped hammerhead shark (Sphyrna lewini) moves through offshore Atlantic water beyond the Carolina coast. The broad cephalofoil spreading from its head contains electroreceptors capable of detecting faint electrical signals produced by prey hidden beneath sand and low-visibility water. | Image credit: A. Murch
Scalloped hammerheads often move in schools, particularly when younger, and feed heavily on fish, squid, and smaller sharks. Their body shape and behavior are well suited for highly mobile pelagic hunting where prey concentrations shift constantly with temperature and current boundaries.
They are not simply “using deeper water.” They are adapted to a system where the structure itself is always moving.
Warm and cool water masses sliding against one another can compress bait into narrow feeding corridors. Squid rise toward the surface after dark. Pelagic fish move vertically and horizontally depending on light levels and prey availability. The scalloped hammerhead’s movement patterns mirror that instability.
Because they occupy such mobile offshore environments, scalloped hammerheads help regulate prey populations across broad sections of the continental shelf rather than within a single localized habitat.
The Hidden Hammerhead
For decades, scientists believed many hammerheads moving through the western Atlantic belonged to the same species.
But the Carolina hammerhead (Sphyrna gilberti) had likely been there the entire time unnoticed.
Researchers eventually discovered that some sharks identified as scalloped hammerheads were genetically distinct and consistently possessed fewer vertebrae, revealing that two separate species had been moving through the same waters unnoticed (Quattro et al., 2013).
Radiographs of the Carolina hammerhead (Sphyrna gilberti) (left) helped reveal that a second hammerhead species had been moving through western Atlantic waters largely unnoticed. Although visually similar to the scalloped hammerhead (right), skeletal differences and genetic analysis confirmed the Carolina hammerhead as a distinct species in 2013. | Image credit: J. Quattro et al., 2013 (left); S. Raredon, Smithsonian Institution, National Museum of Natural History (right)
The discovery revealed that even sharks moving through the same Atlantic waters were more specialized than they first appeared.
From the beach, the offshore Atlantic often appears open and uniform because distance hides most of its detail. But even scientists were still uncovering hidden structures within those waters. Sharks that looked nearly identical from the surface were occupying the same coastline as separate species with potentially different ecological roles.
The Carolina hammerhead still overlaps geographically with other hammerheads along the southeastern United States, and researchers are continuing to study how those species divide habitat, prey, and movement through the Atlantic.
For beachgoers, the discovery is a reminder that the Atlantic beyond the breakers is more ecologically layered than it first appears, with multiple shark species occupying waters that can look uniform from shore.
The Ray Hunter
The great hammerhead (Sphyrna mokarran) occupies a different ecological role than its smaller relatives.
A great hammerhead shark (Sphyrna mokarran) moves through offshore water. The species is highly specialized for hunting rays, using its broad cephalofoil to improve maneuverability and detect prey hidden along the seafloor. | Image credit: Oregon State University
Great hammerheads are more solitary and strongly associated with rays, including stingrays and cownose rays. Their cephalofoil is not simply a sensory structure. It also improves maneuverability and may help pin rays against the seafloor during feeding attempts (Strong et al., 1990).
That specialization matters because rays themselves strongly influence coastal ecosystems.
Rays such as cownose rays and Atlantic stingrays disturb sediment, expose buried organisms, and alter benthic communities while feeding across shallow coastal bottoms. Great hammerheads help regulate those ray populations and influence where rays spend time feeding.
Great hammerheads influence more than the number of rays moving through coastal habitats. The presence of large predators changes prey behavior as well. Rays may avoid lingering in exposed feeding areas when hammerheads are nearby, redistributing feeding pressure across habitats.
For beachgoers, those ecological effects may eventually appear through changes in ray abundance, feeding activity, or shifting patterns of disturbed sediment along shallow coastal waters.
The Cooler-Water Hunter
The smooth hammerhead (Sphyrna zygaena) can look, at first glance, like another variation of the same hammerhead design.
But its head gives away part of its story.
Unlike the scalloped hammerhead, the smooth hammerhead lacks the central notch along the front edge of the cephalofoil. That difference may seem small to a casual observer, but it reflects a separate species adapted to a somewhat different part of the Atlantic system. Smooth hammerheads are often associated with cooler temperate waters and feed heavily on schooling fish and cephalopods moving through offshore shelf waters (Compagno, 2001).
A smooth hammerhead shark (Sphyrna zygaena) moves through open offshore water. Unlike the scalloped hammerhead, the smooth hammerhead lacks the central notch along the front edge of the cephalofoil and is more commonly associated with cooler temperate waters and schooling prey along the continental shelf. | Image credit: S. Judd
That specialization matters because schooling fish and squid help move energy through the open Atlantic.
These prey species do not stay fixed in one place. They shift with temperature, currents, light, and season, gathering in patches that may appear briefly before dispersing again. Smooth hammerheads are part of the predator community that follows and regulates that movement through cooler portions of the continental shelf.
The relationship is not simply a shark chasing fish through open water. By feeding within those moving schools, smooth hammerheads help shape how prey gathers, how long those schools remain concentrated, and how much pressure they place on smaller forage species below them in the food web.
For beachgoers, those ecological effects may eventually appear through seasonal changes in bait movement, bird activity, or the mix of predators feeding along the shelf as offshore waters warm and cool through the year.
The Shark That Connects Habitats
Few sharks move between offshore and coastal systems as fluidly as the tiger shark.
Tiger sharks (Galeocerdo cuvier) are often reduced in public imagination to sensational headlines or descriptions as “garbage eaters,” largely because of their opportunistic feeding behavior and willingness to consume a wide range of prey.
But ecological flexibility is precisely what makes them important.
A tiger shark (Galeocerdo cuvier) moves through tropical offshore water. Tiger sharks travel between offshore habitats, shoals, and coastal systems following seasonal prey movements, linking distant parts of the Atlantic food web through their wide-ranging movements and opportunistic feeding behavior. | Image credit: Fishes of Sarasota County, FL
Tiger sharks move between offshore waters, shoals, nearshore habitats, and sometimes estuarine environments following seasonal prey movements and temperature shifts (Heithaus, 2001). Sea turtles, rays, fish, carrion, and other prey species all become part of that broader movement pattern.
Their presence changes how other animals use the same habitats.
Sea turtles may avoid grazing too heavily in exposed areas when tiger sharks are nearby. Rays redistribute feeding activity. Schools of fish alter where they gather. The presence of a large predator changes how long prey species remain in one place and how intensely they feed before moving on. Areas that might otherwise experience constant grazing or disturbance begin receiving periods of recovery as animals move more cautiously through the habitat (Heithaus et al., 2008).
That movement connects habitats that people often think of as separate parts of the ocean.
A tiger shark feeding offshore may later move closer to shoals, estuaries, or coastal waters as prey shifts with season and temperature. The same predator influencing sea turtle grazing patterns offshore may eventually pass along the edges of bait schools closer to shore weeks later.
For beachgoers, those connections may appear through changing patterns of sea turtle activity, shifting schools of fish near the breakers, or the seasonal movement of predators along the Carolina coast.
The Sharks People Talk About Most
Not all sharks connected to Onslow County remain far offshore.
Species like the great white shark and bull shark tend to dominate public attention because they are more familiar through media coverage and coastal sightings. Tagged great whites moving along the Atlantic coast frequently make headlines, while sharks seen near inlets or murky water are often assumed to be bull sharks whether identification is confirmed or not.
But those assumptions can flatten the complexity of the coastal ecosystem.
Bull sharks (Carcharhinus leucas)are well known for their ability to tolerate freshwater, but they are not the only sharks capable of handling changing salinity. Along the Carolina coast, species such as bonnetheads and juvenile hammerheads also use estuarine environments where tides, rainfall, and river flow constantly shift the balance between salt and fresh water. Coastal systems are not divided into simple categories of “ocean” and “freshwater.” They are gradients, and many sharks are adapted to move through those changing conditions.
A bull shark (Carcharhinus leucas) moves through offshore water accompanied by remoras. Although bull sharks are known for their ability to tolerate lower salinity and move into estuaries and rivers, they are also highly mobile coastal and offshore predators that regularly travel through marine waters along the Atlantic coast. | Image credit: B. Skinstad
Great whites (Carcharodon carcharias), meanwhile, are often discussed as solitary coastal hunters, but along the western Atlantic they are also highly migratory predators tied to seasonal prey movements, temperature ranges, and offshore habitats (Block et al., 2011).
A great white shark (Carcharodon carcharias) moves through open offshore water. Great whites are highly migratory predators capable of traveling vast distances between offshore habitats and productive coastal feeding grounds, linking distant regions of the Atlantic and Pacific through seasonal movement. | Image credit: E. Levy
Both species are part of the broader Atlantic system connected to North Carolina’s coast, but the sharks occupying pelagic waters beyond the visible horizon often receive far less attention despite shaping offshore food webs just as strongly.
Why Recovery Takes So Long
Many fish species along the Carolina coast mature quickly and reproduce in enormous numbers. Menhaden, mullet, and other forage fish may begin reproducing within only a few years while releasing hundreds of thousands—or even millions—of eggs.
Large sharks follow a very different strategy.
Species like great hammerheads, tiger sharks, and threshers often require more than a decade to reach reproductive maturity, and they produce far fewer offspring than most bony fish (Cortés, 2000). Some large female sharks may spend well over a decade surviving storms, fishing pressure, predators, disease, and changing ocean conditions before producing pups for the first time.
That slower reproductive strategy evolved partly because large sharks occupy upper levels of the food web where adults face relatively few natural predators. Evolution favored longer lifespans, slower growth, and fewer offspring with higher survival chances.
But the same strategy creates vulnerability.
A fish population capable of reproducing within two or three years can rebound relatively quickly after declines. A shark population that requires fifteen years or more to produce breeding adults cannot.
The offshore Atlantic built these predators slowly.
And when populations decline, recovery happens slowly as well.
Why More Sightings Do Not Always Mean More Sharks
For many people along the Carolina coast, sharks can feel more visible now than they did decades ago.
Drone footage from the North Carolina coast reveals how modern technology now captures shark movement near beaches that would have gone largely unseen from shore only a few decades ago. Increased visibility does not necessarily mean sharks are suddenly overwhelming coastal waters, but it does change how people perceive the Atlantic around them. | Image credit: L. Abed
Anglers report more sharks taking hooked fish before they can be reeled in, a behavior known as depredation. Drone footage captures feeding activity that would have gone unseen from shore years ago. Social media spreads sightings quickly, sometimes creating the impression that sharks are suddenly overwhelming coastal waters.
Some shark populations have shown signs of recovery following decades of decline and changing fishing regulations. Long-time fishers noticing more shark encounters in certain areas may not be imagining it. In some cases, there likely are more sharks present than there were during periods of heavier population decline in the late twentieth century.
But recovery is not the same as overabundance.
Forty years ago, far fewer people were fishing offshore, kayaking through estuaries, filming the surf with drones, or posting shark encounters online in real time. Coastal waters are now observed more continuously than at any point in history, while recreational fishing activity itself creates more opportunities for sharks and people to interact.
Even with signs of recovery, many large shark species along the Atlantic coast still exist at a fraction of the population levels seen before major declines in the late twentieth century (Baum et al., 2003; Worm et al., 2013).
A true overabundance of large predators would likely look very different along the Carolina coast. Bait schools would become harder to find, feeding activity along the surface would begin thinning out, and predators would increasingly compete over limited prey. Instead, much of what people are witnessing today is the overlap between recovering shark populations, concentrated recreational fishing activity, and a coastline watched more closely than ever before (Heithaus et al., 2008).
For beachgoers, that change can make sharks feel suddenly more common, even as many offshore ecosystems are still rebuilding from declines that unfolded over generations.
What Changes Along the Coast When They Decline
By the time most people arrive at the beach in summer, the offshore system is already in motion.
Pelicans are not simply following random schools of fish. The bait moving through the breakers may have spent weeks feeding along temperature boundaries farther offshore. Rays passing through the shallows are connected to predators that hunt them beyond the visible edge of the continental shelf. Squid rising toward the surface at night become part of a food web that stretches from deep Atlantic water back toward the surf zone.
Most of those connections remain invisible from shore.
A person standing on the beach cannot see a bigeye thresher moving through dim offshore water hundreds of feet below the surface, or a hammerhead sweeping across the bottom searching for the electrical signals of buried prey. They cannot see tiger sharks shifting between offshore and coastal habitats as water temperatures change through the season.
But those predators still influence what eventually reaches the coastline.
The schools of fish birds gather over, the movement of rays through shallow water, the distribution of predators and prey along the continental shelf, and even the timing of seasonal feeding activity are tied to an offshore ecosystem organized partly by sharks most people never encounter directly.
From the beach, the Atlantic often appears flat and open beyond the horizon.
In reality, it is layered with movement, specialization, and predators adapted to parts of the ocean most people never realize are there.
What the Horizon Conceals
From the beach, the Atlantic often appears flat and empty beyond the breakers. Most people will never see a bigeye thresher rising from dim offshore water or a hammerhead sweeping across the continental shelf searching for prey hidden beneath the sand. The larger structure of the pelagic Atlantic remains mostly invisible from shore.
But the absence of visibility is not the same as absence of life.
Far beyond the swimming beaches and nearshore bars, sharks continue moving through layered offshore habitats shaped by depth, temperature, migration, and prey. Some travel between offshore waters and shoals. Others patrol deeper pelagic systems where sunlight fades and the surface reveals little of what exists below.
Those movements eventually connect back to the coast itself.
The same Atlantic that carries sea turtle hatchlings past the breakers, pushes baitfish toward the shoreline, and gathers pelicans over feeding fish also extends outward into a far larger offshore ecosystem organized by predators most people never see directly.
The horizon does not separate the beach from another ocean.
It only marks the point where the visible Atlantic gives way to the hidden one.
Even from the shoreline, the Atlantic extends into a far larger offshore ecosystem shaped by predators, migration, depth, and movement beyond what can easily be seen from shore. The horizon does not mark the end of the ocean’s structure, only the limit of what we can observe from the beach. | Image credit: A. Mitchell
References
Baum, J. K., Myers, R. A., Kehler, D. G., Worm, B., Harley, S. J., & Doherty, P. A. (2003). Collapse and conservation of shark populations in the Northwest Atlantic. Science, 299(5605), 389-392. https://doi.org/10.1126/science.1079777
Block, B. A., Jonsen, I. D., Jorgensen, S. J., Winship, A. J., Shaffer, S. A., Bograd, S. J., Hazen, E. L., Foley, D. G., Breed, G. A., Harrison, A., Ganong, J. E., Swithenbank, A., Castleton, M., Dewar, H., Mate, B. R., Shillinger, G. L., Schaefer, K. M., Benson, S. R., Weise, M. J., … Costa, D. P. (2011). Tracking APEX marine predator movements in a dynamic ocean. Nature, 475(7354), 86-90. https://doi.org/10.1038/nature10082
Compagno, L. J. (2001). Sharks of the world: An annotated and illustrated catalogue of shark species known to date (2nd ed.). Food and Agriculture Organization of the United Nations.
Heithaus, M. R. (2001). The biology of tiger sharks, Galeocerdo Cuvier, in Shark Bay, Western Australia: Sex ratio, size distribution, diet, and seasonal changes in catch rates. Environmental Biology of Fishes, 61(1), 25-36. https://doi.org/10.1023/a:1011021210685
Heithaus, M. R., Frid, A., Wirsing, A. J., & Worm, B. (2008). Predicting ecological consequences of marine top predator declines. Trends in Ecology & Evolution, 23(4), 202-210. https://doi.org/10.1016/j.tree.2008.01.003
Kajiura, S. M. (2001). Head morphology and Electrosensory pore distribution of Carcharhinid and Sphyrnid sharks. Environmental Biology of Fishes, 61(2), 125-133. https://doi.org/10.1023/a:1011028312787
Klimley, A. P. (1993). The Behavior and Ecology of the Scalloped Hammerhead Shark. Stanford University Press.
Oliver, S. P., Turner, J. R., Gann, K., Silvosa, M., & D’Urban Jackson, T. (2013). Thresher sharks use tail-slaps as a hunting strategy. PLoS ONE, 8(7), e67380. https://doi.org/10.1371/journal.pone.0067380
Quattro, J. M., Driggers, W. B., Grady, J. M., Ulrich, G. F., & Roberts, M. A. (2013). Sphyrna gilberti, a new hammerhead shark (Carcharhiniformes, Sphyrnidae) from the western Atlantic Ocean. Zootaxa, 3702(2), 159. https://doi.org/10.11646/zootaxa.3702.2.5
Sims, D. W. (2006). Differences in habitat selection and reproductive strategies of male and female sharks. Sexual Segregation in Vertebrates, 127-147. https://doi.org/10.1017/cbo9780511525629.009
Strong, W. R., Snelson, F. F., & Gruber, S. H. (1990). Hammerhead shark predation on Stingrays: An observation of prey handling by Sphyrna mokarran. Copeia, 1990(3), 836. https://doi.org/10.2307/1446449
Worm, B., Davis, B., Kettemer, L., Ward-Paige, C. A., Chapman, D., Heithaus, M. R., Kessel, S. T., & Gruber, S. H. (2013). Global catches, exploitation rates, and rebuilding options for sharks.
Sometimes the estuary changes before people notice why.
The water may look normal from shore, but drifting just beneath the surface are long ribbons of translucent gelatin — soft strands that gather along marsh edges, collect in eddies, or drift through the current like mucus suspended in the tide. In Surf City this week, people described them as “whale snot.”
Gelatinous material collected from Murrells Inlet, South Carolina at the low tide edge. Such suspended material may include colonial tunicates, salps, mucus-rich plankton aggregates, and other organic matter associated with productive estuarine conditions. | Image credit: J. Mattevi
They are more likely colonial tunicates or salps, gelatinous filter-feeders that can appear suddenly when conditions in the water favor rapid plankton growth (Bone, 1998; Madin & Deibel, 1998).
What matters is not only the organisms themselves, but what their appearance says about the estuary around them.
The drifting forms
These blooms often form when the water column becomes temporarily stable and productive (Madin, 1982). Warmer temperatures, calmer conditions, reduced wave turbulence, and elevated plankton concentrations create an environment where filter-feeding gelatinous organisms can reproduce rapidly. Water moving through the inlets may also transport offshore plankton communities into the estuary, concentrating them in tidal creeks and slower-moving surface water (Bone, 1998; Madin, 1982).
In these calmer stretches, the water column begins separating into layers. Suspended plankton remains concentrated near the surface while weaker turbulence allows fragile gelatinous colonies to persist long enough for blooms to form. What would normally disperse through wave action instead remains suspended within the estuary itself (Madin, 1982).
To most people, they look like debris.
Ecologically, they are processing the estuary in real time.
Salps and colonial tunicates continuously pump water through their bodies, removing suspended phytoplankton, bacteria, and organic particles from the water column. During bloom periods, enormous volumes of water can be filtered each day (Madin, 1982; Sutherland et al., 2010). In effect, the estuary briefly develops a drifting layer of living filtration suspended between the surface and the bottom.
Each colony filters continuously. Thousands moving through a tidal creek or marsh edge at once can collectively filter enormous volumes of suspended material over short periods of time, temporarily altering the clarity and composition of the surrounding water (Riisgård & Larsen, 2010).
That shift affects everything around them.
When these blooms are abundant, water clarity can temporarily improve as suspended particles are removed. Organic material becomes concentrated into mucus-rich waste pellets and decaying gelatinous tissue that sink toward the bottom, transferring energy from the surface into benthic food webs below (Madin & Deibel, 1998). Microbes, worms, crustaceans, and scavengers begin responding almost immediately (Madin, 1982; Madin & Deibel, 1998).
Instead of remaining suspended near the surface, nutrients and organic matter begin settling downward through the water column. What had been dispersed through open water becomes concentrated along the bottom, where deposit-feeding worms, small crustaceans, microbes, and scavengers begin incorporating that material into the estuary below (Madin, 1982).
The bloom itself becomes food.
The drifting masses also create temporary structure within otherwise open water. Small fish gather along their edges. Tiny invertebrates gather within folds and strands of gelatinous tissue. Predators begin responding not only to the bloom itself, but to the concentration of life forming around it (Bone, 1998; Madin & Deibel, 1998).
Small fish and invertebrates feed around the edges of these drifting masses. Juvenile fishes may remain near these drifting masses as food becomes concentrated around them. Sea turtles, some fishes, and other gelatinous predators may increase feeding activity where blooms become dense enough to concentrate prey (Bone, 1998).
But like many ecological events, balance matters.
If too few filter-feeders are present during periods of elevated nutrients, water grows murkier and oxygen conditions become less stable, particularly during heat and nighttime respiration. But filtration at the opposite extreme can also reshape the food web. Too many gelatinous filter-feeders, however, may strip large amounts of plankton from the water column, altering food availability for larval fishes and other plankton-dependent organisms higher in the food web (Petersen & Riisgård, 1992).
Most blooms are temporary.
Currents disperse them. Heat and bacteria break them apart. Waves fragment the colonies into nearly invisible strands that disappear back into the system as quickly as they arrived. Even in collapse, the bloom continues feeding the estuary. Decaying tissue is broken apart by bacteria, consumed by scavengers, and recycled back into the same nutrient pathways that allowed the bloom to form in the first place (Madin, 1982).
But for a short period, the estuary reveals something normally hidden: the water between the marsh and the bottom is not empty space. It is an active habitat, filled with organisms that filter, recycle, transport, and redistribute energy through the coastal ecosystem (Bone, 1998; Madin, 1982).
The attached forms
Not all tunicates remain suspended in the water column. Some attach themselves directly to the surfaces that hold still long enough for life to accumulate—dock pilings, oyster shell, ropes, marsh grass roots, floats, and the shaded undersides of piers where current continues moving but turbulence drops away.
Along the estuaries of Onslow County, these attached forms become part of what looks, at first glance, like simple buildup.
The surfaces beneath docks rarely stay bare for long (Wahl, 1989; Lindeyer & Gittenberger, 2011). Marine scientists often describe these layered growths as fouling communities, but along the estuary they appear simply as the layer of life that forms on anything left in the water long enough. First comes a film too thin to notice, then algae, then colonies of organisms layered over one another until wood, shell, and rope begin carrying part of the estuary itself.
Sea squirts and other attached filter-feeders beneath a dock in Surf City, North Carolina. | Image credit: A. Mitchell
Tunicates are part of that layer.
Along this coast, attached tunicates can include solitary species like the pleated sea squirt (Styela plicata) and the sea grape (Molgula manhattensis), as well as colonial species such as Clavelina oblonga and sea pork (Aplidium stellatum) (Van Name, 1945; Lambert, 2007).
Some grow individually, attached like soft sacs with openings at the top. Others spread as colonial sheets or clustered lobes, sharing a common outer covering while continuously filtering water moving past them. Around pilings and floating docks, entire communities can form this way—sponges beside hydroids, bryozoans layered against tunicates, all responding to current, salinity, temperature, and suspended food moving through the tide (Wahl, 1989).
To most people, these surfaces register as slime.
Ecologically, they are filtration, habitat, and nutrient transfer occurring simultaneously (Wahl, 1989).
Sea squirts
The organisms most people recognize first are usually sea squirts. They appear as rubbery sacs attached beneath docks or clustered along ropes, and shell. Press one accidentally and water jets outward through small siphons near the top of the body, giving rise to the common name.
A sea squirt partially coated in algae and sediment beneath shallow estuarine water in Surf City, North Carolina. The two siphon openings are part of the continuous filtration process occurring beneath docks and marsh edges. | Image credit: A. Mitchell
Species such as the pleated sea squirt (Styela plicata) often develop thick, wrinkled outer coverings ranging from tan and off-white to purple, while the sea grape (Molgula manhattensis) forms smaller rounded bodies attached within the layered communities growing beneath docks and along estuarine structure — what marine scientists often call fouling communities (Van Name, 1945).
What looks like a reaction is actually the visible end of a process already underway.
Sea squirts continuously pull water inward through one siphon, filter out phytoplankton, bacteria, and suspended particles from the water, then expel the filtered water back into the estuary through another opening. The animal does not begin filtering when disturbed. It has been filtering the entire time (Riisgård & Larsen, 2010).
In productive estuarine water, thousands of these organisms may be pumping simultaneously (Riisgård & Larsen, 2010).
That filtration matters.
As suspended particles are removed, nutrients become concentrated into waste and biomass that can be transferred downward into bottom communities. Water clarity may improve locally (Riisgård & Larsen, 2010). Microbial activity shifts around them. Small invertebrates begin using the folds and surfaces their bodies create.
Their presence also signals something about the surrounding water.
Sea squirts tend to cluster where flow remains steady enough to deliver oxygen and suspended food continuously, but not so violent that colonies are torn free. Around tidal creeks, dock edges, and quieter stretches of the Intracoastal Waterway, their abundance often reflects a system carrying enough suspended productivity to sustain constant filtration (Barros, 2009).
Sea pork
Some tunicates take a different form entirely.
One of these is sea pork, commonly associated with colonial tunicates such as Aplidium stellatum, which spread outward as shared gelatinous colonies rather than isolated individuals (Van Name, 1945).
Sea pork, a colonial tunicate, washed ashore along Surf City, North Carolina. Though it appears as a single gelatinous mass, it is made up of thousands of tiny filter-feeding animals embedded within a shared outer layer. | Image credit: D. Miles
Sea pork spreads across submerged surfaces in thick, rubbery colonies that look less like individual animals and more like flesh-colored mats attached beneath floats and pilings. Depending on the species and age of the colony, the surface may appear muted pink, tan, orange, or almost translucent beneath the waterline.
Most people don’t realize they are looking at colonies made up of thousands of tiny individual filter-feeding bodies embedded together within a shared outer layer.
The colony functions collectively (Van Name, 1945).
Water moves continuously through countless small openings across the surface, carrying suspended plankton and organic particles into the colony while waste and filtered water move back outward into the surrounding estuary (Riisgård & Larsen, 2010).
That structure changes the surface around it.
Sea pork colonies trap sediment and create small protected surfaces where microorganisms and invertebrates begin to accumulate between folds and protected edges. Tiny crustaceans move across them. Worms and microbial films develop within the folds and protected spaces between colonies. What appears smooth from above becomes, at smaller scales, complex terrain (Wahl, 1989).
Like other filter-feeding communities along this coast, sea pork helps transfer suspended energy from the water column into the attached world beneath docks and marsh edges.
And once that layered habitat forms, other organisms begin responding to it—including the nudibranchs moving slowly across its surface.
Nudibranchs
At low tide along the edges of the sound—where pilings hold a thin skin of life and oyster shells stack into uneven ridges—the water sometimes carries color that doesn’t belong to the sand or the grass. It moves slowly, almost deliberately, across surfaces that most people step over without noticing. What looks like a fragment of drifting algae or a soft piece of shell resolves, if you stop long enough, into something alive.
These are nudibranchs.
They are not fish, not worms, not plants. They are marine gastropods—relatives of snails—but without shells (Valdés et al., 2006). Along the coast of Onslow County, they appear in the quiet places: beneath docks in the Intracoastal Waterway, along the edges of Topsail Island marsh creeks, and on the submerged surfaces where current slows just enough for growth to take hold.
Along shallow estuarine structure in this region—beneath docks, across pilings, and within the layered growth attached to ropes and shell—nudibranchs may include species such as the striped nudibranch (Cratena pilata), the Brazilian aeolid sea slug (Spurilla braziliana), the fringeback dondice (Dondice occidentalis), Thecacera pennigera, Berghia rissodominguezi, and the brackish-water species Tenellia adspersa (Marcus, 1972; Valdés et al., 2006).
Most people never see them. But they are there, working through the same system that shapes everything else along this coast.
A nudibranch collected near Morehead City, North Carolina, viewed under magnification. The cerata along its back increase surface area for respiration and, in some species, store defensive stinging cells obtained from prey. | Image credit: marineinvertgirl, iNaturalist
Built for sensing, not speed
A nudibranch’s body is built for sensing and feeding, not speed. The two structures at the front—rhinophores—sample the water chemically, reading it the way a shoreline bird reads the wind. Along their backs, many species carry cerata, small extensions that look ornamental but function as both respiration and defense.
In aeolid nudibranchs like Spurilla braziliana, Cratena pilata, and Berghia rissodominguezi, these cerata become important sites for both respiration and defensive storage of stinging cells obtained from prey (Goodheart et al., 2018).
The Brazilian aeolid sea slug (Spurilla braziliana) moving across submerged structure near Morehead City, North Carolina. The cerata lining its back function in respiration and can store defensive stinging cells obtained from prey such as anemones and hydroids. | Image credit: wonglab, iNaturalist
They move slowly because they can afford to. Their food doesn’t run.
Sponges, hydroids, bryozoans—these are the surfaces most people would describe as “growth” on docks or shells. To a nudibranch, those surfaces are structure, habitat, and food all at once (Valdés et al., 2006).
The work they do (even when no one’s watching)
Along this coastline, growth is constant. Give any hard surface—an old piling, a piece of shell, a boat hull—enough time in the water and it becomes layered. First a film, then algae, then invertebrates. The system builds upward and outward, creating what scientists call structural complexity, but what you actually see is texture: roughness where there used to be smoothness (Wahl, 1989).
Along shallow estuarine bottoms, algae, shell, and attached growth begin forming the layered habitat that supports juvenile fish, crabs, filter-feeders, and the organisms moving through the estuary food web. | Image credit: A. Mitchell
Nudibranchs move through that texture selectively.
Many species feed on a single type of prey. One may specialize in a particular sponge. Another tracks hydroids, those delicate branching animals that resemble tiny underwater ferns. Species such as Dondice occidentalis, Cratena pilata, and Tenellia adspersa are commonly associated with hydroids and other organisms growing across submerged pilings, docks, ropes and shell in shallow coastal environments (Marcus, 1972; Valdés et al., 2006). This selectivity matters more than their size suggests. They are not removing everything. They are removing specific pieces of the system.
That kind of feeding does not flatten the landscape—it shapes it.
Where one organism begins to dominate, nudibranchs can limit its spread. Where surfaces would otherwise become uniform, their grazing introduces variation. Over time, this helps maintain the uneven habitat small fish, shrimp, and juvenile invertebrates depend on (Wahl, 1989).
Growth that begins as algae quickly becomes habitat. Along shallow estuarine edges, layered vegetation and attached organisms create shelter for crabs, juvenile fish, shrimp, and other small life moving through the system. | Image credit: A. Mitchell
It’s easy to miss because nothing dramatic happens. There’s no visible clearing, no sudden absence. But the balance of what grows, and where, shifts quietly in response to their presence.
Borrowed defenses, redistributed energy
Some nudibranchs do something that seems improbable until you see it up close: they take the defenses of what they eat and keep them.
Hydroids and certain cnidarians carry stinging cells—nematocysts—that function as protection. When a nudibranch feeds on them, those cells pass through the digestive system intact and are stored within the cerata along its back. The nudibranch doesn’t just consume its prey; it incorporates part of its defense (Goodheart et al., 2018).
This changes how energy moves through the system.
Instead of defenses being lost when prey is consumed, they are transferred upward. The nudibranch becomes both grazer and deterrent, a small organism that is less likely to be eaten because of what it has already eaten.
You can see the result in their coloration. Many are bright, almost out of place against the muted tones of sand and shell. That color is not decoration—it’s a signal (Avila, 1995). Along this coast, where predation pressure is constant, visibility can function as warning rather than risk.
Where they sit in the trophic cascade
They are not apex predators. They don’t regulate fish populations or move through the system in ways that draw attention. But they occupy a position that connects the base of the food web to everything above it.
They feed on organisms that build habitat.
Those organisms—sponges, hydroids, bryozoans—form the living surface that supports small invertebrates and juvenile fish. Those smaller organisms, in turn, become prey for larger fish, which then connect to the predators people are more familiar with along this coast—species like blacktip shark (Carcharhinus limbatus) and Atlantic sharpnose shark (Rhizopriodion terranovae) that move along the breakers and through the sounds.
Remove the visible predators, and people notice quickly.
Remove something like a nudibranch, and what changes is slower, but it moves in the same direction. Surfaces become dominated by fewer species. Habitat becomes more uniform. The small organisms that rely on variation lose space. That change works its way upward, not as a single event, but as a shift in the system’s capacity to support diversity.
Even small organisms attached to pilings and submerged structure become part of much larger coastal food webs. Scientific food-web models show nudibranchs, hydroids, bryozoans, worms, shrimp, and fishes linked together through the transfer of energy across the ecosystem.
Generalized food web showing how organisms associated with sponge and attached invertebrate communities connect upward through coastal ecosystems. Nudibranchs, hydroids, bryozoans, worms, shrimp, and fishes all participate in the transfer of energy through these layered habitats. Adapted from Archer et al. (2020).
Why they stay hidden
There’s a reason most beachgoers never encounter them.
They live where water movement slows just enough to allow growth to accumulate, but not so still that oxygen drops away. Around docks, inside creeks, along the quieter edges of the New River estuary, they remain attached to the surfaces that feed them.
Out in the open surf, where sand shifts constantly and hard structure is buried and exposed with each change in wind and tide, there’s less for them to hold onto and less for them to eat. The breakers are a moving environment (Wahl, 1989). Nudibranchs belong to the places that hold still just long enough for complexity to form.
What changes if they’re gone
Nothing you would notice in a single afternoon at the beach.
But over time, the surfaces beneath the waterline would begin to simplify. One or two fast-growing organisms would spread further, covering space that would otherwise remain shared. The small sheltered spaces used by larval fish, juvenile shrimp, and small crabs would begin to thin out.
That loss doesn’t stay at the bottom.
It moves upward, changing how much life the system can support, and how evenly that life is distributed. By the time it reaches the fish people see from the shore, the cause is no longer visible. But it started here, in the slow movement of something small across a surface most people never look at twice.
Nudibranchs don’t reshape the coastline in ways that draw attention. They don’t mark their presence with absence or disturbance. Instead, they work within what’s already there—adjusting, redistributing, and maintaining the uneven structure that makes this coast function.
If you happen to see one, it won’t be moving fast. It won’t need to.
What they’re feeding on (and why it looks familiar)
Along the docks and pilings of Onslow County, the surfaces most people notice first aren’t fish at all. They’re the things attached to everything.
The branching, plant-like fuzz that brushes your hand when you reach into the water—those are hydroids. The firm, uneven coatings that look like they’re part of the structure itself are often sponges or bryozoans.
It’s easy to group all of it together as buildup. Something slimy, something in the way.
But that “squirt” people laugh about isn’t random. A tunicate pulls water in, filters out plankton and suspended particles, and then expels that water back out. What looks like a reaction is just the visible end of constant filtration. They are processing the water column—removing particles, cycling nutrients, and clarifying the water in small, continuous ways (Riisgård & Larsen, 2010).
Hydroids are doing something different. They are predators at a scale most people don’t consider, capturing microscopic prey drifting past. Sponges filter continuously as well, pulling bacteria and organic matter from the water and converting it into biomass that other organisms can use.
A sea anemone beneath shallow estuarine water in Surf City, North Carolina. Organisms like these become part of the layered communities that nudibranchs, tunicates, hydroids, and other invertebrates move through beneath the surface. | Image credit: A. Mitchell
This is the surface layer of the ecosystem. And it doesn’t stay unchecked.
The ones moving across the surface
Species like the Brazilian aeolid sea slug (Spurilla braziliana) often feed directly on anemones associated with these same submerged communities, while smaller species such as Tenellia adspersa are frequently associated with hydroids in brackish and estuarine waters (Valdés et al., 2006).
The nudibranchs moving across these surfaces are not all the same, and what they eat tells you what role they’re playing.
Some of the small, leaf-like sea slugs in this region—species in the genus Elysia—feed on algae and can even retain the chloroplasts from what they consume, briefly using sunlight as part of their energy system. They blur the line between grazing and something closer to plant-like function (Valdés et al., 2006).
Others, like Cratena pilata and Dondice occidentalis, track hydroids specifically. Where hydroids begin to spread across a piling, these nudibranchs follow, feeding in a way that limits how dense those colonies can become (Marcus, 1972).
Species such as Thecacera pennigera are often associated with the layered communities growing beneath docks and harbor structure, while Berghia rissodominguezi and Spurilla braziliana move through shallow cnidarian-rich habitat where anemones and hydroids provide both food and defensive material (Valdés et al., 2006).
Heavier-bodied nudibranchs—often in groups like Doris—tend to feed on sponges. Not all sponges, and not everywhere, but selectively enough that no single form easily dominates a surface for long.
Even their eggs reflect this connection. The ribbon-like spirals sometimes seen attached to docks are laid directly where food is available. The next generation doesn’t disperse randomly—it begins where the system is already functioning.
Beneath the surface layer
Most of the time, these organisms go unnoticed.
People see the drifting ribbons and call them whale snot. They scrape tunicates from pilings without thinking about what those colonies were filtering from the water. They brush past hydroids and sponges growing beneath docks without realizing those surfaces are part of the estuary’s food web just as much as the fish moving above them.
But the water between the marsh and the bottom is never empty.
It carries suspended plankton, drifting larvae, dissolved nutrients, bacteria, predators, scavengers, and colonies of organisms filtering continuously through the tide. Along the quieter edges of Onslow County—beneath floats, around oyster shells, beside marsh grass roots, and inside the slower water of creeks and sounds—entire communities form within that suspended layer (Wahl, 1989; Lindeyer & Gittenberger, 2011).
Some drift. Some attach. Some graze slowly across the surface consuming the organisms beneath them.
Together, they reshape the estuary constantly.
The gelatinous ribbons appearing this week are not separate from the rest of the system. They are one visible moment in a larger cycle of filtration, growth, decay, grazing, and redistribution that normally happens out of sight (Bone, 1998; Madin, 1982). For a short time, the estuary simply becomes easier to see.
What appears empty from above often contains layered communities of algae, filter-feeders, invertebrates, and microorganisms quietly redistributing energy through the estuary. Surf City, North Carolina. | Image credit: A. Mitchell
References
Avila, C. (1995). Natural products of opisthobranch molluscs: A biological review. In Oceanography and marine biology: An annual review (33rd ed., pp. 487-559). UCL Press.
Barros, R. (2009). Human-mediated global dispersion of Styela plicata (Tunicata, Ascidiacea). Aquatic Invasions, 4(1), 45-57. https://doi.org/10.3391/ai.2009.4.1.4
Bone, Q. (1998). The biology of pelagic tunicates. Oxford University Press on Demand.
Encarnação, J., Seyer, T., Teodósio, M. A., & Leitão, F. (2020). First record of the nudibranch Tenellia adspersa (Nordmann, 1845) in Portugal, associated with the invasive hydrozoan Cordylophora caspia (Pallas, 1771). Diversity, 12(6), 214. https://doi.org/10.3390/d12060214
Goodheart, J. A., Bleidißel, S., Schillo, D., Strong, E. E., Ayres, D. L., Preisfeld, A., Collins, A. G., Cummings, M. P., & Wägele, H. (2018). Comparative morphology and evolution of the cnidosac in Cladobranchia (Gastropoda: Heterobranchia: Nudibranchia). Frontiers in Zoology, 15(1). https://doi.org/10.1186/s12983-018-0289-2
Korshunova, T., Lundin, K., Malmberg, K., Picton, B., & Martynov, A. (2018). First true brackish-water nudibranch mollusc provides new insights for phylogeny and biogeography and reveals paedomorphosis-driven evolution. PLOS ONE, 13(3), e0192177. https://doi.org/10.1371/journal.pone.0192177
Lambert, G. (2007). Invasive sea squirts: A growing global problem. Journal of Experimental Marine Biology and Ecology, 342(1), 3-4. https://doi.org/10.1016/j.jembe.2006.10.009
Lindeyer, F., & Gittenberger, A. (2011). Ascidians in the succession of marine fouling communities. Aquatic Invasions, 6(4), 421-434. https://doi.org/10.3391/ai.2011.6.4.07
Madin, L. P. (1982). Production, composition and sedimentation of salp fecal pellets in oceanic waters. Marine Biology, 67(1), 39-45. https://doi.org/10.1007/bf00397092
Petersen, J., & Riisgard, H. (1992). Filtration capacity of the ascidian Ciona intestinalis and its grazing impact in a shallow fjord. Marine Ecology Progress Series, 88, 9-17. https://doi.org/10.3354/meps088009
Riisgård, H., & Larsen, P. (2010). Particle capture mechanisms in suspension-feeding invertebrates. Marine Ecology Progress Series, 418, 255-293. https://doi.org/10.3354/meps08755
Sutherland, K. R., Madin, L. P., & Stocker, R. (2010). Filtration of submicrometer particles by pelagic tunicates. Proceedings of the National Academy of Sciences, 107(34), 15129-15134. https://doi.org/10.1073/pnas.1003599107
Valdés, Á., Behrens, D. W., & DuPont, A. (2006). Caribbean Sea slugs: A Field guide to the opisthobranch mollusks from the tropical Nortwestern Atlantic. Sea Challengers Natural History Books.
Van Name, W. G. (1945). The North and South American Ascidians. Bulletin of American Museum of Natural History, 84, 1-476. http://hdl.handle.net/2246/1186
Wahl, M. (1989). Marine epibiosis. I. Fouling and antifouling: Some basic aspects. Marine Ecology Progress Series, 58, 175-189. https://doi.org/10.3354/meps058175
