Sharks of Onslow County

Tag: trophic cascade

Blue Land Crabs Near Onslow County: What to Watch For and What Their Presence Could Change

The Hole at the Grass Line

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

Christy, J. H. (1982). Burrow structure and use in the sand fiddler crab, Uca pugilator (Bosc). Animal Behaviour, 30(3), 687-694. https://doi.org/10.1016/s0003-3472(82)80139-5

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

NC Dept. of Environmental Quality. (2026, August 26). Please report blue land crab sightings. https://www.deq.nc.gov/news/press-releases/2026/08/26/please-report-blue-land-crab-sightings

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

September 5, 2026
The Atlantic Mud Crab and the Marsh Periwinkle Snail

Along the edge of a North Carolina salt marsh, some of the easiest animals to find are also among the easiest to overlook.

Small spiral shells cling to smooth cordgrass, sometimes only inches above the mud and sometimes surprisingly high along the stems. These are marsh periwinkles, Littoraria irrorata, and where they sit changes as the tide moves beneath them. Nearby, oyster shells collect along creek edges and among the vegetation. Beneath one of them may be an Atlantic mud crab, Panopeus herbstii, tucked into a space barely larger than its body.

Neither seems capable of influencing much beyond the few inches it occupies.

Yet the relationship between these two small animals reaches into the grass around them, the sediment beneath them, and eventually the ability of a salt marsh to maintain itself as water levels change.

Both are also indicator species. Their abundance, where they occur, and how they respond to the conditions around them can offer clues about the health of the marsh they share (Fowler & Kingsley-Smith, 2015; Rietl et al., 2018).

For someone walking a boardwalk, paddling a tidal creek, or looking across the marsh on the way to the beach, that makes them particularly interesting. Much of what keeps a salt marsh functioning happens underground, underwater, or so gradually that we never see it happening.

These two animals give us something we can actually watch.

The Snails on the Grass

The marsh periwinkle spends much of its life following the tide up and down the cordgrass.

Marsh periwinkle, Littoraria irrorata. Small enough to fit in the palm of a hand, this marsh snail spends much of its life moving up and down cordgrass with the tide. | Image credit: A. Mitchell

At lower tides, the snails move down the stems and closer to the marsh surface to feed. When the tide comes back in, fish, crabs, and other aquatic predators come with it. The periwinkles respond by climbing higher on the grass, putting distance between themselves and the hunters now swimming below.

So when you see dozens of little snails perched high on the cordgrass beside a flooded marsh, they did not simply choose a nice place to sit.

They have moved upstairs.

As the tide rises, salt marsh periwinkles climb higher on the cordgrass, staying above the water and farther from predators moving through the flooded marsh. | Image credit: andyjones, iNaturalist

That daily trip between the lower grass and the safety of the upper stems is shaped partly by predators. Where those predators are more common, periwinkles change where they spend their time and may even develop differently under that continued pressure (Rietl et al., 2018).

When the water falls again, the little climbers come back down.

As the tide falls, periwinkles move back down through the cordgrass toward the marsh surface, where much of their feeding takes place. | Image credit: JunoMoon, iNaturalist

And this is where their job in the marsh becomes especially interesting.

Periwinkles graze across the surface of smooth cordgrass, Spartina alterniflora. One easy way to picture them is as tiny lawnmowers moving through the marsh. They do not clip every blade equally, though. They often favor older, yellowing, or dead cordgrass, helping work through plant material that is already on its way out (Klinges et al., 2025).

But their feeding is not as simple as taking a bite from a blade of grass.

Those scrapes leave small wounds on the cordgrass where fungi can grow. The snails later return to those areas and feed again, consuming the fungal growth along with plant material. When snail numbers and grazing become unusually high, those repeated wounds can contribute to heavier fungal growth and increasing damage to the cordgrass (Silliman & Newell, 2003).

Like a lawn, the important part is not whether the grass is ever cut.

It is how much.

Enough grazing is part of a functioning marsh. Periwinkles belong here, and their feeding is one of many interactions helping shape the plant community. But put too many little lawnmowers in the same patch and they can begin cutting faster than the grass can recover. Cordgrass becomes shorter and thinner, more plant tissue is wounded, and eventually patches can begin to disappear.

Studies in southeastern salt marshes have shown just how far that change can go when predators are removed and periwinkles become unusually abundant. Heavy grazing can contribute to substantial losses of Spartina rather than simply keeping its growth in check (Altieri et al., 2012).

Fewer snails are not automatically better, either. Grazers are part of the balance of the marsh, just as predators are. What matters is that no single part of the relationship overwhelms the others.

And one of the animals helping keep these little lawnmowers in check is usually not up on the grass at all.

It is waiting below.

Beneath the Shell

Atlantic mud crabs, Panopeus herbstii, are much easier to miss.

Atlantic mud crab, Panopeus herbstii. Small, heavily clawed, and easy to miss among shell and mud, this lower-marsh predator helps keep periwinkle grazers in check. | Image credit: nickifal, iNaturalist

If you have ever looked among oyster shells at the lower edge of a marsh creek, you have looked directly into the kind of neighborhood they prefer. Mud crabs tuck beneath shell and stones, move over muddy bottoms, and use shallow burrows along marsh edges. They live in estuaries where the water is never quite the same from one day to the next—saltier during some periods, fresher after heavy rain, warmer through summer and cooler through winter. Atlantic mud crabs are remarkably good at living within those changing conditions (Fowler & Kingsley-Smith, 2015).

Before any of that, however, a mud crab begins life somewhere very different.

A newly hatched crab does not look like the crab hiding beneath an oyster shell. It begins as a tiny larva drifting in the water, carried through the estuary while it develops. Eventually it must leave that drifting life behind and settle somewhere suitable.

Atlantic mud crab larva, Panopeus herbstii. At this stage, the future bottom-dwelling crab is tiny, transparent, and drifting through the estuary before settling into marsh and oyster-shell habitat. | Image credit: True et al., 2020

Finding that place is not entirely luck.

Young mud crabs can respond to signals in the environment that tell them they have reached the kind of habitat where adult crabs live. Oyster shell, rocks, other organisms, and even the thin films of microorganisms coating submerged surfaces can provide chemical and physical clues that encourage the larva to settle and begin the next stage of life (Andrews et al., 2001; Rodriguez & Epifanio, 2000).

Think about what that means for something small enough to drift with the current.

It does not have a map of the marsh.

Instead, the place itself begins to smell and feel right.

Once settled, the crab eventually becomes one of the predators moving through that habitat. Atlantic mud crabs eat oysters, clams, worms, small crustaceans, snails, and whatever other suitable prey they can capture.

And beneath those oyster shells, researchers have found evidence of one meal again and again.

Periwinkles.

In North Carolina salt marshes, researchers found about 80 percent of the Atlantic mud crab lairs they examined beneath live oyster shells. When they looked at prey remains associated with those lairs, marsh periwinkle shells were among the most common finds (Silliman et al., 2004).

Above the shell, the snail moves along the cordgrass.

Below it, the crab waits.

When Predator Meets Grazer

This is where two small animals begin influencing something much larger.

Periwinkles spend part of each tidal cycle higher on the cordgrass, away from aquatic predators. When the water drops and they move lower to feed, they become more accessible to the mud crabs below.

The crabs do not need to climb the grass and chase them.

They simply need to be there when the snails come back down.

Research has shown that Atlantic mud crabs can keep periwinkle numbers lower, and that mud crab predation increases when more periwinkles are available (Silliman et al., 2004). In practical terms, the predator helps keep all of those little lawnmowers from becoming too numerous.

That matters because the crab is indirectly influencing grass it never eats.

More mud-crab predation can mean fewer periwinkles grazing on the cordgrass. Fewer grazers can mean less pressure on the grass. When predators disappear and periwinkles become too abundant, the opposite can happen.

That chain reaction has a scientific name: a trophic cascade.

A change involving a predator works its way through the animals it eats and eventually affects something farther down the food web. In this case, the path is easy to follow:

mud crab → periwinkle → cordgrass.

Studies elsewhere in southeastern salt marshes have shown how dramatic that cascade can become. Where intensive recreational fishing reduced predator numbers, periwinkles became more abundant, grazing increased, and large areas of marsh vegetation were eventually lost (Altieri et al., 2012).

The Atlantic mud crab never takes a bite from the cordgrass.

Yet by eating an animal that does, it helps influence how much grass remains standing.

And keeping that grass standing turns out to matter far beyond the snail and crab.

An empty periwinkle shell may not stay empty for long. Hermit crabs often move into abandoned shells, turning yesterday’s snail home into today’s shelter. | Image credit: A. Mitchell

What the Grass Holds

A salt marsh has to maintain more than vegetation.

It has to maintain ground.

Smooth cordgrass helps slow the water as each tide moves across the marsh. When the water slows, tiny bits of sand, mud, and other material it was carrying can drop out and settle around the grass. Below the surface, the roots and underground stems help hold that ground together, while old plant material breaks down and becomes part of the marsh soil. Little by little, those layers add up and help the marsh keep its height above the water (Reed, 1995; Elsey-Quirk et al., 2011).

That elevation determines how long and how often the marsh floods.

A difference of only a few inches can change the amount of time vegetation spends underwater, the salinity it experiences, and which plants and animals can occupy a particular part of the marsh.

For a marsh facing rising relative sea level, maintaining elevation becomes increasingly important. If sediment deposition and organic-matter accumulation equal or exceed the rate at which the marsh is becoming submerged, vegetation may persist. If elevation cannot keep pace, flooding increases and vegetation can eventually be lost (Reed, 1995).

A salt marsh has a few ways to keep up as water levels rise. It can build upward as new sediment settles among the grass and as roots and other plant material become part of the soil. It can also slowly shift farther inland onto slightly higher ground—if that ground is still available. How well a marsh can do either depends on the place itself: how much sediment reaches it, how well the vegetation is growing, how strong the tides are, how much erosion is occurring, and how quickly local water levels are rising (Kirwan & Mudd, 2012; Fagherazzi et al., 2020).

The important point is that the biological and physical marsh are not separate systems.

The grass affects sediment.

The sediment affects elevation.

Elevation affects flooding.

Flooding affects the plants and animals.

And among the animals affecting that grass are a snail climbing its stems and a crab waiting below.

When the Water Rises Faster

Sea-level rise can feel abstract when we describe it as a number measured in millimeters or as a line on a map showing where water might be decades from now.

A salt marsh makes it easier to understand.

Marsh plants already live with water coming and going every day. They are built for it. But being covered during part of a normal tide is very different from spending more and more time underwater as the average water level rises.

The marsh has two important ways to respond.

It can build upward as sediment and plant material accumulate. Just up the New River at Camp Lejeune, that struggle to maintain marsh elevation can be seen on the ground.

And, where higher undeveloped ground remains beside it, the marsh can gradually move inland.

That second option matters enormously along a developed coastline.

If rising water makes the lowest edge of a marsh increasingly difficult for cordgrass to occupy, suitable marsh vegetation can begin establishing slightly farther inland. Over time, the position of the marsh shifts.

Unless something is already there.

A road does not move uphill for the marsh.

Neither does a house, parking lot, bulkhead, or other hardened shoreline.

When development occupies the higher ground immediately behind a marsh, rising water can begin pressing from one side while development prevents the marsh from moving on the other. Its room to adjust becomes smaller.

What can eventually disappear is not simply an undeveloped patch of grass that might otherwise have held another building.

NOAA’s Sea Level Rise Viewer lets you watch that landward movement—and where it can become constrained—as water levels change.

The marsh was already working.

Salt marshes provide nursery habitat for fishes and crustaceans, trap sediment, store carbon, help stabilize shorelines, and reduce some of the energy moving through shallow coastal water. Their ability to keep doing those things depends upon the marsh itself remaining high enough, vegetated enough, and connected enough to continue functioning (Fagherazzi et al., 2020).

That is one reason decisions about where and how we build along the coast matter beyond the property line.

A marsh does not have to contain a building to have a purpose.

And Then a Storm Arrives

Sea-level rise changes a marsh gradually.

A storm can rearrange parts of it in a day.

Anyone who lives along the North Carolina coast has seen what heavy rainfall alone can do to local water. Creeks swell. Freshwater pours into sounds and estuaries. Salinity drops. A tropical storm or hurricane can add storm surge, waves, erosion, and enough moving water to carry shell, sediment, wrack, and pieces of the marsh itself from one place to another.

Mud can be stripped away from one creek bank and deposited somewhere else.

Oyster shells that were buried may suddenly be exposed.

Shell that once provided hiding places may be covered.

Cordgrass can be flattened, torn loose, buried beneath wrack, or left standing in a slightly different landscape once the water recedes.

Estuary sediments can preserve that history. In North Carolina’s Albemarle estuarine system, sediments record both the slow changes occurring over decades and the sudden rearrangements associated with storms and other major events (Corbett et al., 2007).

For the Atlantic mud crab and periwinkle, those changes can rearrange the places where their relationship happens.

The periwinkle needs the cordgrass.

The mud crab relies on suitable water conditions, prey, and places such as oyster shell and shallow burrows for cover.

Change the grass, move the shell, freshen the water, or reshape the creek edge and the animals must respond to the new version of the marsh that remains.

That does not mean a healthy marsh should never change.

Quite the opposite.

Tides, storms, erosion, sediment deposition, rainfall, and shifting salinity have always been part of coastal marshes.

What matters is whether enough of the living and physical system remains intact for the marsh to adjust afterward.

Two Species That Tell a Larger Story

This is what makes the Atlantic mud crab and marsh periwinkle especially useful animals to know.

They are not simply inhabitants of the marsh. Both have been used as indicators of conditions within the ecosystems they occupy because their abundance, distribution, and responses are connected to environmental conditions and ecological relationships around them (Fowler & Kingsley-Smith, 2015; Rietl et al., 2018).

The periwinkle gives us one view.

It lives directly on the vegetation, responds to tidal flooding and predation, and can exert increasing pressure on cordgrass when predator–prey relationships change.

The Atlantic mud crab gives us another.

Its abundance is associated with habitat structure, prey availability, Spartina characteristics, oyster habitat, temperature, and salinity, while its predation helps influence the abundance of grazers such as the periwinkle (Silliman et al., 2004; Fowler & Kingsley-Smith, 2015).

Together, they give us something particularly interesting.

They allow us to see part of a trophic relationship that reaches from predator to grazer to plant and, through the plant, into processes affecting the physical marsh.

That does not mean finding ten snails instead of five provides a diagnosis of marsh health, or that turning over one oyster shell and finding no crab means something is wrong. Scientific monitoring requires repeated observations, measurements, and knowledge of local conditions.

But it does mean that these animals are worth noticing.

They can make processes that otherwise seem abstract visible.

Periwinkles scattered through the marsh vegetation offer a visible clue to the living community around them. Their numbers and where they occur can help reveal changes in the balance between grazing, predation, and cordgrass health. | Image credit: BioInteractive

Looking at the Marsh Differently

The next time you are beside the salt marsh along Surf City, look at the grass before you look across it.

Find the little spiral shells.

Notice whether the tide is in or out and where the periwinkles are sitting along the stems. Look lower, toward the mud and oyster shell around the creek edge, at the little spaces where a mud crab might disappear.

Then look at the marsh around them.

Is the cordgrass thick and continuous? Are there areas where the edge is eroding? Has a storm moved wrack or exposed new shell? Where does the water reach at high tide, and where does the ground begin rising toward houses, roads, or other development?

Those observations do not turn a beach walk into a scientific survey.

They do something simpler.

They let us recognize that the marsh is alive with relationships, and that some of the smallest animals in it can help us understand why the larger landscape looks the way it does.

Somewhere in that system, a periwinkle climbs higher as the tide comes in.

Below it, an Atlantic mud crab remains hidden among the shell.

Most people walking toward the beach will pass both without ever knowing they are there.

But once you know what connects them, they become two small signs of something much larger happening beneath your feet.

Across the soundside marshes of Surf City, water, vegetation, wildlife, and the developed shoreline exist side by side—each connected to what happens in the marsh between them. | Image credit: A. Mitchell

References

Altieri, A. H., Bertness, M. D., Coverdale, T. C., Herrmann, N. C., & Angelini, C. (2012). A trophic cascade triggers collapse of a salt-marsh ecosystem with intensive recreational fishing. Ecology, 93(6), 1402–1410. https://doi.org/10.1890/11-1314.1

Andrews, W. R., Targett, N. M., & Epifanio, C. E. (2001). Isolation and characterization of the metamorphic inducer of the common mud crab, Panopeus herbstii. Journal of Experimental Marine Biology and Ecology, 261(1), 121–134. https://doi.org/10.1016/S0022-0981(01)00268-4

Corbett, D. R., Vance, D., Letrick, E., Mallinson, D., & Culver, S. J. (2007). Decadal-scale sediment dynamics and environmental change in the Albemarle estuarine system, North Carolina. Estuarine, Coastal and Shelf Science, 71(3–4), 717–729. https://doi.org/10.1016/j.ecss.2006.09.024

Elsey-Quirk, T., Seliskar, D. M., Sommerfield, C. K., & Gallagher, J. L. (2011). Salt marsh carbon pool distribution in a Mid-Atlantic lagoon, USA: Sea level rise implications. Wetlands, 31(1), 87–99. https://doi.org/10.1007/s13157-010-0139-2

Fagherazzi, S., Mariotti, G., Leonardi, N., Canestrelli, A., Nardin, W., & Kearney, W. S. (2020). Salt marsh dynamics in a period of accelerated sea level rise. Journal of Geophysical Research: Earth Surface, 125(8). https://doi.org/10.1029/2019JF005200

Fowler, A., & Kingsley-Smith, P. (2015). Atlantic mud crab, Panopeus herbstii (H. Milne Edwards 1834). Supplemental Volume: Species of Special Conservation Concern, South Carolina State Wildlife Action Plan.

Kirwan, M. L., & Mudd, S. M. (2012). Response of salt-marsh carbon accumulation to climate change. Nature, 489(7417), 550–553. https://doi.org/10.1038/nature11440

Klinges, D. H., Martin, C. W., & Roberts, B. J. (2025). Ecological associations of the coastal marsh periwinkle snail Littoraria irrorata: Field and laboratory evidence of vegetation habitat preferences. PeerJ, 13, e19071. https://doi.org/10.7717/peerj.19071

Reed, D. J. (1995). The response of coastal marshes to sea-level rise: Survival or submergence? Earth Surface Processes and Landforms, 20(1), 39–48. https://doi.org/10.1002/esp.3290200105

Rietl, A. J., Sorrentino, M. G., & Roberts, B. J. (2018). Spatial distribution and morphological responses to predation in the salt marsh periwinkle. Ecosphere, 9(6), e02316. https://doi.org/10.1002/ecs2.2316

Rodriguez, R., & Epifanio, C. E. (2000). Multiple cues for induction of metamorphosis in larvae of the common mud crab, Panopeus herbstii. Marine Ecology Progress Series, 195, 221–229. https://doi.org/10.3354/meps195221

Silliman, B. R., Layman, C. A., Geyer, K., & Zieman, J. C. (2004). Predation by the black-clawed mud crab, Panopeus herbstii, in Mid-Atlantic salt marshes: Further evidence for top-down control of marsh grass production. Estuaries, 27(2), 188–196. https://doi.org/10.1007/BF02803375

August 15, 2026
The Fish That Follows the Tide: American Eels Along the Waters of Onslow County

Most people who see an American eel (Anguilla rostrata) for the first time do not think they are looking at a fish at all.

They appear suddenly in shallow blackwater creeks, beneath dock lights, beside culverts after rain, or slipping through spartina grass at dusk. Long and muscular, they move more like a snake than something belonging to a river. In muddy water they are usually seen only in fragments — a curve disappearing beneath tannin-dark current, or a ripple crossing the surface where something alive passed moments earlier.

Along the coast of Onslow County, American eels have likely moved through these waters longer than the marshes themselves have held their present shape. They pass through tidal creeks, estuaries, freshwater streams, flooded ditches, cypress swamps, and inland rivers, connecting habitats that often seem separate to us but function together as one living system.

And almost no one realizes that every eel seen here began life far out at sea.

Born Beyond the Horizon

The American eel’s life cycle spans thousands of miles, linking the Sargasso Sea, Atlantic coast, estuaries, marshes, rivers, and inland lakes through a single migration that can last decades. | Image credit: U. S. Fish and Wildlife Service

Far offshore, beyond the continental shelf and beyond the visible horizon of North Carolina’s beaches, lies the Sargasso Sea — a warm, rotating gyre of Atlantic water bordered by ocean currents rather than land. This is where American eels spawn, though much of their reproduction still remains one of the great biological mysteries of the Atlantic Ocean (Béguer‐Pon et al., 2015).After hatching, eel larvae drift for months within the Gulf Stream. At this stage they do not yet resemble eels. They are thin, transparent, leaf-shaped organisms called leptocephali, nearly invisible against the open ocean (Wang & Tzeng, 2000).

Leptocephali, the larval stage of the American eel, drift within the Atlantic Ocean currents for months before transforming into glass eels and entering coastal estuaries. | Image credit: hunterefs, iNaturalist

As they approach the coastline, their bodies begin to transform. The broad leaf-like shape narrows into the familiar eel form. Their organs reorganize. Their muscles strengthen. By the time they arrive in estuaries along the Atlantic coast, they have become what scientists call glass eels — small, transparent juveniles that move into tidal rivers and marshes under the cover of darkness (Starks, 2026).

Glass eels, the transparent juvenile stage of the American eel, gather along coastlines before moving inland through estuaries, marshes, and rivers. | Image credit: W. O’Connor

At night in late winter and spring, these glass eels enter coastal waters by the thousands. Most people never notice them. But beneath bridge lights and along quiet marsh edges, tiny transparent bodies gather against the current, moving inland on tides that have repeated for thousands of years.

Some settle into estuaries. Others continue far upriver into freshwater creeks and reservoirs. A single eel may spend decades there before returning once again to the open Atlantic.

As they continue growing, American eels pass through a series of color changes that reflect different stages of their life cycle. Newly arrived glass eels are nearly transparent. Within months they develop pigmentation and become elvers, often showing olive, brown, or yellowish coloration. During the longest phase of their lives they are known as yellow eels, displaying yellow-brown to olive sides with lighter undersides while feeding and growing in estuaries, rivers, and wetlands for years or even decades (ASMFC, 2017; Haro et al., 2000). As they mature and prepare for their return migration to the Sargasso Sea, they transform into silver eels. Their bodies darken along the back, their sides become silvery, and their eyes enlarge — adaptations that help prepare them for life in the open ocean and their final spawning migration (Haro et al., 2000; Tesch & White, 2008).

American eels change dramatically throughout their lives, from transparent leptocephali and glass eels to yellow eels in estuaries and rivers before developing the silver coloration of spawning adults returning to the Sargasso Sea. | Image credit: C. Bowser & R. Papish

The Marsh at Night

American eels are largely nocturnal, which means many people living along the coast rarely realize how common they are.

After sunset, they emerge from submerged roots, oyster reefs, marsh undercuts, rock piles, and mud-bottom channels to feed. In tidal creeks around Onslow County, they move through habitats that shift constantly with salinity, rainfall, temperature, and tide.

Unlike many fish that specialize in one narrow environment, eels are remarkably flexible. They can tolerate freshwater, brackish estuaries, and saltwater marsh systems throughout different stages of life (Able, 2005).

This flexibility makes them important ecological connectors between habitats.

An eel feeding in an estuary may consume shrimp, small fish, crabs, worms, insect larvae, and carrion. Larger eels become predators capable of feeding on nearly anything they can overpower. In turn, they become prey themselves for river otters, wading birds, striped bass, sharks, alligators, ospreys, and larger coastal predators (MacGregor et al., 2009).

What appears at first to be a strange solitary fish is actually woven through multiple levels of the food web.

American eels help transfer energy through the ecosystem, linking marsh invertebrates, small fish, and larger predators with the waters of Onslow County. | Image credit: A. Mitchell

Ancient Currents and Modern Coastlines

And in a much deeper sense, eels also connect modern coastal ecosystems to ancient worlds that existed long before humans reshaped shorelines. Their lineage stretches back tens of millions of years, surviving repeated shifts in sea level, climate, and continental geography. Long before beach renourishment projects, before the Outer Banks existed in their present form, and even before many modern mammals evolved, ancestral eels were already moving between oceans and coastal rivers (Inoue et al., 2010).

That timeline overlaps surprisingly well with the broader environmental history explored in my earlier posts. During the Carboniferous Period over 300 million years ago, vast swamp forests covered portions of what would eventually become eastern North America, laying down the organic material that later formed coal deposits (Sahney et al., 2010). The world looked entirely different then, but the shallow coastal environments that support migratory fish today evolved from ancient marine systems shaped across those immense spans of geologic time.

By 66 million years ago — around the end-Cretaceous extinction that eliminated non-avian dinosaurs — early eel relatives already existed in ancient seas (Near et al., 2012). Modern American eels evolved much later, but their migratory strategy reflects something extraordinarily old: the continual exchange between ocean currents, estuaries, rivers, and wetlands.

Fossil eels resembling modern species appear in the geologic record tens of millions of years ago, reflecting a lineage that has persisted through changing oceans, shifting coastlines, and repeated cycles of environmental change. | Image credit: Fossil Forum

Beach renourishment, by contrast, exists on an almost microscopic timescale geologically. Most projects reshape shorelines over years or decades, temporarily altering sediment movement, inlet dynamics, turbidity, and nearshore habitat. Eels are resilient enough to survive natural coastal change — hurricanes, shifting barrier islands, overwash events, and migrating inlets that have continually transformed the Atlantic coast. But human-driven shoreline modification can compress those disturbances into shorter, more frequent intervals that affect how juvenile eels enter estuaries and move inland.

So while beach renourishment itself is modern, the habitats it alters are part of a coastal system assembled over millions of years — one that species like the American eel have been navigating since long before the present coastline existed.

Their ecological importance is recognized even within local fisheries. In many areas, crab pots are now designed with eel escapement openings that allow smaller American eels to exit traps rather than become unintended bycatch. These modifications help reduce eel mortality while acknowledging the species’ role in maintaining healthy estuarine ecosystems.

The Animal That Connects Rivers

Many coastal species remain tied to a single environment. Oyster reefs remain fixed in estuaries. Marsh periwinkle snails cling to grass stems. Flounder shift between nearshore and estuarine waters but remain marine fish.

American eels move between worlds.

A juvenile eel may travel from offshore Atlantic currents into a coastal marsh creek, then into freshwater rivers hundreds of miles inland before eventually returning to the Sargasso Sea years later to spawn. Very few animals along the Atlantic coast connect ecosystems across such enormous distances.

American eels connect ecosystems across the Atlantic Ocean, beginning life in the Sargasso Sea before dispersing into estuaries, rivers, lakes, and wetlands throughout eastern North America. } Image credit: L. Poirier

Because of this, eels transport energy and nutrients between habitats that otherwise remain loosely connected. Predators feeding on eels receive marine-derived nutrients that originated far offshore. When adult eels migrate back toward the Atlantic, they carry inland energy back toward the ocean system (Jessop et al., 2020).

Even freshwater mussels depend upon them.

Several mussel species release microscopic larvae called glochidia that temporarily attach to fish hosts while developing. Research in Mid-Atlantic rivers has shown that American eels are one of the most successful hosts for some native mussel species, helping sustain mussel populations throughout eastern river systems (Schwalb et al., 2013).

So beneath the surface, the eel is doing more than surviving for itself. It is helping move life through the watershed.

What Happens When Eels Decline

Globally, the American eel is listed as “endangered, but stable” on the IUCN Red List because of long-term population declines across much of its range (IUCN, 2023). In the United States, however, the U. S. Fish and Wildlife Service has concluded the species does not currently require federal protection under the Endangered Species Act. The Atlantic States Marine Fisheries Commission determined that their populations are largely depleted in U. S. waters and have recommended continued monitoring of their populations because their life cycle depends upon the health and connectivity of both freshwater and marine environments (ASMFC, 2026).

For centuries, rivers along the Atlantic coast held far larger eel populations than they do today.

In many parts of the eastern United States, dams and hydroelectric turbines block migration routes and kill adults moving back downstream toward the ocean. Those barriers have severely reduced eel access to inland habitat across major river systems (Haro et al., 2000).

Onslow County is different.

The New River estuary is not fed by large mountain rivers or controlled by dams upstream. It is a relatively closed coastal watershed shaped instead by rainfall, groundwater springs, blackwater creeks, tidal exchange, runoff, and low-gradient streams winding through wetlands and forests. Here, eel movement depends less on navigating massive river barriers and more on the health and connectivity of marshes, culverts, floodplains, tidal creeks, and shallow estuarine habitat.

That makes local environmental changes especially important.

Wetland loss, shoreline hardening, stormwater runoff, dredging, declining water quality, and altered tidal flow can fragment the smaller pathways eels rely upon throughout the watershed. Even undersized culverts or poorly designed drainage structures can interrupt movement between creeks and flooded wetlands during critical migration periods.

Barrier islands also shape the system eels enter.

Along the Onslow coast, shifting inlets, overwash events, and beach renourishment projects continually reshape the boundary between ocean and estuary. In some cases, renourishment can temporarily increase turbidity, bury nearshore habitat, or alter tidal exchange patterns affecting juvenile eel recruitment into estuarine creeks. At the same time, healthy barrier islands and functioning marsh systems help buffer salinity extremes, reduce erosion, and maintain the sheltered estuarine habitat young eels depend upon once they arrive from the Atlantic.

Because eels use so many habitats, their decline spreads outward through the ecosystem in ways people may not immediately notice.

River otters lose an important prey source in some waterways. Mussel reproduction declines where host fish disappear. Predators that once relied seasonally on eels shift toward other prey. The disappearance of a species that connects marshes, rivers, estuaries, and offshore currents weakens the ecological ties between those environments.

And unlike species that reproduce quickly, eels recover slowly.

An eel living beneath a dock in coastal North Carolina may already be older than the child fishing above it. Some females remain inland for decades before ever returning to spawn (Haro et al., 2000). Every interruption between inland waters and the sea disrupts a migration pattern older than modern coastlines themselves.

The Fish Most People Never See

On warm summer nights in coastal North Carolina, much of the estuary moves unseen.

Shrimp rise into the water column. Rays cross shallow mudflats beneath darkness. Juvenile fish gather around dock lights. Crabs emerge from oyster beds to forage with the tide.

And somewhere below that shifting water, an eel moves silently between habitats, carrying the Atlantic inland and returning inland waters back toward the sea.

Most people standing along the shoreline will never know it is there.

But the marsh still holds the traces of its passage. So do the river otters weaving through flooded reeds and the herons stalking the quiet creek edges at dusk.

The tidal creeks of Onslow County continue shaping themselves around an animal whose life still stretches beyond much of human observation — from blackwater rivers to the open Atlantic, and back again.

Hidden beneath dark water and shifting tides, American eels remain one of the Atlantic coast’s most remarkable connections between ocean, estuary, and river. | Image credit: E. Smith, iNaturalist

References

Able, K. W. (2005). A re-examination of fish estuarine dependence: Evidence for connectivity between estuarine and ocean habitats. Estuarine, Coastal and Shelf Science, 64(1), 5-17. https://doi.org/10.1016/j.ecss.2005.02.002

ASMFC. (2026). American Eel. Atlantic States Marine Fisheries Commission. https://asmfc.org/species/american-eel/

Béguer-Pon, M., Castonguay, M., Shan, S., Benchetrit, J., & Dodson, J. J. (2015). Direct observations of American eels migrating across the continental shelf to the Sargasso Sea. Nature Communications, 6(1). https://doi.org/10.1038/ncomms9705

Haro, A., Richkus, W., Whalen, K., Hoar, A., Busch, W., Lary, S., Brush, T., & Dixon, D. (2000). Population decline of the American eel: Implications for research and management. Fisheries, 25(9), 7-16. https://doi.org/10.1577/1548-8446(2000)025<0007:pdotae>2.0.co;2

Inoue, J. G., Miya, M., Miller, M. J., Sado, T., Hanel, R., Hatooka, K., Aoyama, J., Minegishi, Y., Nishida, M., & Tsukamoto, K. (2010). Deep-ocean origin of the freshwater eels. Biology Letters, 6(3), 363-366. https://doi.org/10.1098/rsbl.2009.0989

Jessop, B. M. (2020). Oceanic environmental effects on American eel recruitment to the east river, Chester, Nova Scotia. Marine and Coastal Fisheries, 12(4), 222-237. https://doi.org/10.1002/mcf2.10121

MacGregor, R., Casselman, J. M., Allen, W. A., Haxton, T., Dettmers, J. M., Mathers, A., LaPan, S., Pratt, T. C., Thompson, P., Stanfield, M., Marcogliese, L., & Dutil, J. D. (2009). Natural Heritage, Anthropogenic Impacts, and Biopolitical Issues Related to the Status and Sustainable Management of American Eel: A Retrospective Analysis and Management Perspective at the Population Level. American Fisheries Society Symposium, 69, 713-740. https://www.thelandbetween.ca/wp-content/uploads/2014/06/Anacat_Final_Final-reprint_-macgregor.pdf

Near, T. J., Eytan, R. I., Dornburg, A., Kuhn, K. L., Moore, J. A., Davis, M. P., Wainwright, P. C., Friedman, M., & Smith, W. L. (2012). Resolution of ray-finned fish phylogeny and timing of diversification. Proceedings of the National Academy of Sciences, 109(34), 13698-13703. https://doi.org/10.1073/pnas.1206625109

Pike, C., Casselman, J., Crook, V., DeLucia, M. B., Jacoby, D., & Gollock, M. (2023). Anguilla rostrata. The IUCN Red List of Threatened Species. https://dx.doi.org/10.2305/IUCN.UK.2023-1.RLTS.T191108A129638652

Sahney, S., Benton, M. J., & Falcon-Lang, H. J. (2010). Rainforest collapse triggered Carboniferous tetrapod diversification in Euramerica. Geology, 38(12), 1079-1082. https://doi.org/10.1130/g31182.1

Schwalb, A. N., Cottenie, K., Poos, M. S., & Ackerman, J. D. (2011). Dispersal limitation of unionid mussels and implications for their conservation. Freshwater Biology, 56(8), 1509-1518. https://doi.org/10.1111/j.1365-2427.2011.02587.x

Starks, C. (2026). Interstate Fisheries Management Program Overview: American Eel (May 2026). Atlantic States Marine Fisheries Commission. https://asmfc.org/wp-content/uploads/2025/11/4.AmericanEel_May-2026.pdf

Tesch, F. W., & White, R. J. (2008). The eel (5th ed.). John Wiley & Sons.

Wang, C., & Tzeng, W. (2000). The timing of metamorphosis and growth rates of American and European eel leptocephali: A mechanism of larval segregative migration. Fisheries Research, 46(1-3), 191-205. https://doi.org/10.1016/s0165-7836(00)00146-6

May 29, 2026
Beyond the Horizon: The Pelagic Sharks Off Onslow County

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.

Cortés, E. (2000). Life history patterns and correlations in Sharks. Reviews in Fisheries Science, 8(4), 299-344. https://doi.org/10.1080/10408340308951115

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.

Musick, J. A., Burgess, G., Cailliet, G., Camhi, M., & Fordham, S. (2000). Management of sharks and their relatives (Elasmobranchii). Fisheries, 25(3), 9-13. https://doi.org/10.1577/1548-8446(2000)025<0009:mosatr>2.0.co;2

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

Weng, K. C., & Block, B. A. (2004). Diel vertical migration of the bigeye thresher shark (Alopias superciliosus), a species possessing orbital retia mirabilia (102:221–229). NMFS Scientific Publications Offic. https://spo.nmfs.noaa.gov/sites/default/files/pdf-content/2004/1021/weng.pdf

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.

May 22, 2026
Where Wings Meet Water: Reading Birds Along the Edges of Onslow County

At the Line Where Air Meets Water

On a late spring morning along Surf City, the first movement is often above the water, not within it. Brown pelicans travel low and steady just beyond the breakers, their wingtips nearly touching the surface as they follow a line that seems invisible from shore. Farther out, a group of terns holds in place against the wind, hovering, adjusting, then dropping sharply into the water before rising again. Closer to the sound side of Topsail Island, an osprey circles once, then folds into a dive toward a channel edge that looks, at first glance, no different than the water around it.

Nothing about these movements is random. They are responses to structure that exists beneath the surface—structure shaped by tide, wind, and the movement of other organisms. What appears as scattered bird activity is, in practice, a map of where the water is concentrating life.

For someone standing at the edge of it, that movement is one of the most accessible ways to read what cannot be seen directly.

What Birds Are Following Beneath the Surface

The birds that move along this stretch of coast are not searching broadly; they are tracking concentration. Along barrier island systems like those in Onslow County, physical processes—tidal exchange through inlets, wind-driven surface currents, and subtle differences in bottom shape—create zones where small fish, shrimp, and other prey accumulate (Peterson & Peterson, 1979; Piersma, 1997).

When the tide moves through places like New River Inlet, water does not flow evenly across the landscape. It accelerates through constrictions, slows along marsh edges, and bends around sandbars and channels. These shifts in speed and direction compress organisms into tighter spaces, particularly along boundaries where moving water meets something that resists it—an edge, a drop-off, or a change in depth (Wright et al., 1985).

Small schooling fish respond to that compression by tightening their formation. In doing so, they become more visible and more vulnerable. Larger fish—bluefish, Spanish mackerel, and juvenile coastal sharks—often move in from below, using that same concentration to feed. The pressure from below pushes prey upward, sometimes all the way to the surface.

Coastal birds feeding where prey has been concentrated near the surface along the breakers. | Image credit: A. Mitchell

What appears overhead depends on which part of that concentration each species is built to exploit.

Terns hovering and diving are often responding to prey that has been driven upward by predatory fish (Safina & Burger, 1985). Brown pelicans, which rely on plunge-diving, tend to follow more stable schools of fish that remain near the surface for longer periods (Shields, 2014). Ospreys, in contrast, depend on clear water and individual fish they can visually isolate, which is why their activity often aligns with calmer conditions and defined channel edges (Poole et al., 2002).

Each species is not simply feeding in the same place; each is reading a different layer of the same system.

When Surface Activity Signals Pressure Below

From the shoreline, bird activity can appear as isolated events—one dive, then another, then a sudden shift down the beach. Watched over time, a pattern emerges. A cluster of terns may concentrate in one location for several minutes, then disperse abruptly, reforming farther along the shoreline. Pelicans may align along a narrow band just beyond the breakers, following it as it drifts.

These shifts often reflect changes in how prey is being compressed and released beneath the surface. When predatory fish move through a bait school, the school tightens, rises, and becomes briefly accessible from above. When that pressure dissipates, the school spreads out again, and the birds move on.

This movement of energy—from smaller organisms to larger predators, and upward through the water column—is one visible expression of a trophic cascade. The term itself is often used to describe longer chains of ecological influence, but along the coast it can be observed in compressed moments, where the effects of predation become visible within seconds (Heithaus et al., 2008).

Birds do not initiate this process. They respond to it. Their presence marks where the system has already intensified.

Indicator Species at the Water’s Edge

From the beach, the difference is subtle. The water does not change color dramatically, and the waves continue to break as they did before. The level of activity shifts within that band—first visible in the air, then inferred below– marking places where the system has tightened, energy is moving through multiple layers at once, and the distance between surface and depth has, for a time, narrowed (Heithaus et al., 2008; Estes et al., 2011).

For someone entering the water, these differences in bird behavior can offer practical information, not in a predictive or absolute sense, but as indicators of what is happening just below the surface.

Brown pelicans traveling low in a consistent line often indicate schools of fish moving parallel to shore. Terns repeatedly diving in a tight area suggest smaller prey being pushed upward, frequently by larger fish feeding below. Ospreys focusing on a specific channel edge reflect clearer water and individual prey availability, rather than broad schooling events. Along the shoreline, shorebirds probing the sand at low tide are responding to invertebrates exposed by receding water, signaling a different layer of the system entirely—one tied to sediment and tidal timing rather than active predation (Colwell, 2010; Piersma, 1997).

None of these signals point directly to a specific species beneath the surface. What they indicate is concentration, and concentration is what draws larger predators closer to shore.

Along the coast of North Carolina, nearshore and juvenile shark presence is often associated with areas of high prey density, particularly where schooling fish aggregate (Heupel & Hueter, 2002). These conditions are not constant, and they shift with tide, temperature, and time of day. Birds make those shifts visible in real time.

At times, that activity stretches into lines that run the length of the breakers.

For someone stepping into the water, that narrowing matters. Not as a warning in the abstract, but as a recognition that the conditions supporting visible feeding above often extend below, linking organisms that are rarely seen together into the same moving structure.

Where the System Tightens

The patterns become easier to see near places where the water is forced to narrow, turn, or accelerate. The most consistent bird activity along this coast tends to occur where water movement is constrained and redirected. Inlets, marsh edges, sandbars, and the transitions between the Intracoastal Waterway and adjacent sounds create these zones (Wright et al., 1985).

At New River and its inlet, tidal flow compresses water into narrow channels before releasing it into broader areas, creating gradients in speed and depth. Along these gradients, prey accumulates, predators follow, and birds gather above.

These are not fixed points. As tide rises and falls, and as wind reshapes surface conditions, the locations of these compression zones shift. The birds move with them, tracing patterns that are constantly changing but not random.

For someone watching from shore, these movements can be read as lines, clusters, and absences—places where activity intensifies, and places where it suddenly drops away.

Standing Within It

Entering the water along this coast means stepping into a system already in motion. The surface may appear uniform, but the activity above it often reveals where that motion is focused.

Birds diving repeatedly in a confined area, or tracking a narrow band just beyond the breakers, indicate where prey is concentrated. Those same conditions are what draw larger predators into closer proximity to shore, not as an anomaly, but as part of the same process.

Watching the birds does not eliminate risk, and it does not provide certainty about what is beneath the surface. What it offers is context—a way to recognize when the water is more active, more compressed, and more connected across its layers.

What appears as feeding from above is part of a larger structure moving through the water. The birds do not create it, and they do not remain once it passes. They mark it, briefly, making visible what is otherwise difficult to see.

Bird movement along the shoreline often draws attention toward activity that remains unseen beneath the surface. | Image credit: A. Mitchell

References

Castro, J. I. (1993). The shark nursery of bulls Bay, South Carolina, with a review of the shark nurseries of the southeastern coast of the United States. Environmental Biology of Fishes, 38(1-3), 37-48. https://doi.org/10.1007/bf00842902

Colwell, M. A. (2010). Shorebird ecology, conservation, and management. University of California Press.

Estes, J. A., Terborgh, J., Brashares, J. S., Power, M. E., Berger, J., Bond, W. J., Carpenter, S. R., Essington, T. E., Holt, R. D., C. Jackson, J. B., Marquis, R. J., Oksanen, L., Oksanen, T., Paine, R. T., Pikitch, E. K., Ripple, W. J., Sandin, S. A., Scheffer, M., Schoener, T. W., & Wardle, D. A. (2011). Trophic downgrading of planet Earth. Science, 33(6040), 301-306. https://doi.org/10.1126/science.1205106

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

Heupel, M. R., & Hueter, R. E. (2002). Importance of prey density in relation to the movement patterns of juvenile blacktip sharks ( Carcharhinus limbatus ) within a coastal nursery area. Marine and Freshwater Research, 53(2), 543-550. https://doi.org/10.1071/mf01132

Peterson, C. H., & Peterson, N. M. (1979). Ecology of intertidal flats of North Carolina: A community profile (79/39). FWS/OBS. https://pubs.usgs.gov/publication/fwsobs79_39

Piersma, T. (1997). Do global patterns of habitat use and migration strategies Co-evolve with relative investments in Immunocompetence due to spatial variation in parasite pressure? Oikos, 80(3), 623-631. https://doi.org/10.2307/3546640

Poole, A. F., Bierregaard, R. O., & Martell, M. S. (2002). Osprey (Pandion haliaetus). In The Birds of North America (1st ed.). Cornell Lab of Ornithology.

Safina, C., & Burger, J. (1985). Common tern foraging: Seasonal trends in prey fish densities and competition with bluefish. Ecology, 66(5), 1457-1463. https://doi.org/10.2307/1938008

Shields, M. (2014). Brown Pelican (Pelecanus occidentalis). In Birds of North America (1st ed.). Cornell Lab of Ornithology.

Wright, L., Short, A., & Green, M. (1985). Short-term changes in the morphodynamic states of beaches and surf zones: An empirical predictive model. Marine Geology, 62(3-4), 339-364. https://doi.org/10.1016/0025-3227(85)90123-9

May 9, 2026
Alligators in North Carolina Coastal Waters: What Their Presence Really Means

The Surface That Holds

There are mornings along the edges of the water in Onslow County when the surface looks still enough to trust.

The marsh grass has not yet reached its summer height. What stands there leaves more water exposed between the stems, and without sustained wind, the surface holds its shape. You can see farther into it now than you will in a few weeks, before suspended sediment and constant movement return it to opacity. The water carries less of the season, and because of that, more of what moves beneath it becomes visible—if you are willing to wait long enough to see the difference between movement and reflection.

This is when people begin to notice them again.

Not all at once. Not everywhere. Just a change that does not follow wind or tide. A line that holds where the rest of the surface releases. Something that holds its position in a system that is always adjusting.

An alligator does not arrive in that moment.

It becomes visible.

Alligator emerging from the mud. | Photo credit: Gilbert Grant, iNaturalist

Seasonal Absence Is Not Absence

Through winter, they remain within these same creeks, marsh edges, and quieter channels. What changes is not location, but how they occupy it. As temperatures fall, activity narrows. Movement slows, and the need for it slows with it. Energy is conserved, not spent. And the surface carries fewer signs of what lies beneath it. Individuals hold in deeper water or along softer margins where mud retains heat longer than the surrounding water column, remaining within conditions that allow them to persist without constant movement (Nifong et al., 2014; Rosenblatt & Heithaus, 2011).

The same stretch of water that in spring will hold a visible form can pass through winter without interruption, its stillness mistaken for absence.

But the system does not empty.

It compresses.

The System Wakes in Layers

By early spring, that compression begins to release—not all at once, but in layers that build on each other before they are recognized. Shallow water warms first, taking in solar heat more quickly than deeper channels. Along these edges, fish begin to hold longer. Movements that in winter passed through quickly begin to extend into areas that had remained quiet. Invertebrates return to the sediment surface, and the water column begins to carry more suspended life, even before it becomes visible as turbidity.

Birds respond to this before most other changes are noticed. Their movements tighten. Landings become more frequent, departures more abrupt. What they are tracking is not random. It is the redistribution of energy into places where it can be accessed.

The alligator moves within that shift.

Not as a trigger. Not as something layered on top. But as part of a system reorganizing itself across temperature, light, and movement at the same time.

Great blue heron and alligator are part of an interconnected system. | Photo credit: Audubon North Carolina

Reading What It Is Responding To

When one becomes visible along the edge of a creek or marsh, it is easy to reduce that moment to temperature alone. Warmer water allows for more activity.

But what draws it into that position is more specific than warmth.

It is the arrangement of prey.

Along the margins where water meets land, movement compresses. Fish traveling with the tide encounter shallow gradients that limit how long they can remain. Small mammals moving between marsh and upland must cross exposed edges. Birds landing to feed do so in places where depth and access align for only short intervals.

These are not isolated events. They are recurring patterns shaped by tidal cycles, substrate, and seasonal change.

The alligator positions itself within those patterns.

Its diet reflects that flexibility, spanning invertebrates, fish, birds, reptiles, and mammals depending on size and availability (Nifong, 2016). But the diet alone does not explain its placement. What matters is where energy becomes concentrated, even briefly.

That concentration is not constant. It forms and dissolves with tide, with light, with movement.

And the predator tracks that.

And what appears as a single movement—a fish turning, a bird lifting, something crossing the edge of the marsh—is part of a larger structure that holds only briefly before dissolving again.

The alligator does not respond to the individual movement.

It responds to the pattern that produces it.

Where Freshwater Meets Salt

These are not just places where water mixes.

They are places where movement is forced—and where that movement becomes available to something waiting at the top of it.

There are places along this coastline where those changes concentrate.

At the mouths of creeks, along the edges of the Intracoastal Waterway, and near the shifting bars of New River Inlet, the water does not settle into a single condition. Freshwater moves outward with tide and rainfall, meeting saltwater pressing back in with tidal exchange. The result is not a fixed boundary, but a gradient that shifts continuously—sometimes visible as a faint line, sometimes only detectable in how the surface moves differently from one side to the other.

This is where alligators are most often encountered—because this is where the system compresses into something they can use.

They are not marine animals. They do not possess the specialized salt glands that allow for extended life in high salinity environments. Over time, saltwater carries a physiological cost, requiring a return to freshwater to restore balance (Rosenblatt & Heithaus, 2011; Fujisaki et al., 2014).

But that limitation does not exclude them.

It defines how they move through them.

In these mixing zones, salinity is not constant. It rises and falls with tide, with rainfall, with wind direction. A location that carries higher salinity at one stage may shift toward fresher conditions hours later. What appears to be a boundary is, in practice, a moving field.

Within that field, movement compresses.

Fish traveling with the tide are funneled into narrower pathways. Shallow gradients limit how long they can remain in deeper water. Schools tighten. Individuals encounter edges that restrict escape. The system concentrates energy into space.

The predator does not need to range widely in these conditions.

It needs to hold where movement is forced.

And so it does.

An alligator near the tall grass near Marine Corps Air Station New River | Photo credit: Martin Egnash

At the Edge of the Open Water

There are moments when that pattern extends beyond the mixing zones, into places that appear, at first, outside of where an alligator belongs.

Along the shoreline, in the breaking waves where the ocean meets sand, one will sometimes appear—rising and falling with the swell, holding position just beyond where the water turns over onto the beach. It looks misplaced, as though it has moved beyond the system that defines it.

It has not.

The surf zone is one of the most compressed environments along the coast. Waves reduce depth, disrupt orientation, and concentrate movement into a narrow band where escape is limited. Fish pushed into breaking water lose some ability to maintain direction. Schools fragment. Individuals become briefly exposed in ways that do not occur in deeper, more stable water.

For a predator capable of stillness followed by short bursts of movement, that compression creates opportunity.

But the cost is higher.

Salinity is elevated. The water is in constant motion. There is no stable refuge within immediate reach. Time in this environment cannot be extended indefinitely.

And so it does not.

Movements into higher salinity water tend to be brief—extensions outward, followed by a return to freshwater or lower salinity conditions where balance can be restored (Nifong et al., 2014).

What appears as an anomaly is part of a larger pattern.

The predator crosses the boundary not to remain, but to use it, moving where the system briefly offers more than it costs.

The same forces that shape the marsh edge—compression, constraint, and brief exposure—are recreated here, just for a moment, in a different place.

An alligator rests at the ocean’s edge in North Topsail. | Photo credit: Fox8 Digital Desk

What Its Presence Changes

Most of what that presence changes cannot be seen when it is observed.

Long before any direct interaction occurs, it is already altering how other organisms use space.

Fish moving along the edge do not simply pass through. They adjust their depth, their speed, the amount of time they remain exposed. Birds land with shorter intervals between contact and departure. Mammals approaching the water shift their paths or their timing. These changes are not dramatic in isolation. But they are continuous.

Over time, they accumulate into structure—the kind that determines who feeds, where they feed, and how long they remain.

The influence of a predator at this level extends beyond what it consumes. It shapes behavior across multiple species, redistributing where and how energy moves through the system. The possibility of predation—present even when not observed—alters interactions in ways that regulate access to habitat and resources (Heithaus et al., 2008; Ripple et al., 2014; Estes et al., 2011).

What holds the system in place is not removal alone.

It is pressure.

What is being shaped is not just movement, but access—and access is what determines how energy moves through the system.

More Than Predation

The influence of the alligator does not end with what it hunts, but extends beyond those interactions.

As it moves through shallow systems, it disturbs sediment, creating depressions and pathways that alter how water is retained and how nutrients are redistributed. These small changes in physical structure create conditions that other species use—temporary refuges, feeding areas, and zones where organic material accumulates (Eversole et al., 2018; Subalusky et al., 2009).

In wetland systems, these disturbances have been linked to broader effects, including nutrient cycling and carbon storage, where the presence of large predators contributes to the retention of organic material within the system rather than its export (Murray et al., 2025; Atwood et al., 2015).

These processes do not occur in isolation.

They intersect with the same patterns of movement, feeding, and behavior that define the system at larger scales.

Seeing the Surface, Reading the System

When one becomes visible along the surface, it is easy to treat the moment as singular.

A sighting. An encounter. Something separate from everything around it.

But that form at the surface is supported by layers extending beyond what can be seen.

It reflects water temperatures crossing into ranges that support sustained activity. It reflects prey moving into positions where access becomes possible. It reflects a system where behavior is still shaped by the presence of something at the top.

The alligator is not an interruption to that system.

It is an expression of it.

What Becomes Visible

Seeing one does not indicate that something has entered the water.

It indicates that enough beneath the surface is functioning to hold it.

Not in a static sense. Not as balance in the way it is often described. But as a set of interactions that remain connected—movement, response, pressure—each shaping the others even when they are not directly observed.

What becomes visible at the surface is only a fraction of that structure.

But it is enough to know that the rest is still in place.

An alligator in Onslow County sits at the edge of the saltmarsh. |Photo credit: Gilbert Grant, iNaturalist

When That Pressure Is Reduced

If that pressure is reduced, the system does not leave an obvious gap.

It shifts.

Movements that were once constrained begin to extend. Species that passed quickly through exposed areas begin to remain longer. Edges that functioned as transition zones become used differently—not because the physical environment has changed, but because the conditions that shaped behavior within it have relaxed.

Mid-level predators expand their activity under these conditions, increasing their access to prey and space when not constrained from above (Nifong et al., 2013).

The change is subtle.

It appears in how long something stays. In how often it returns. In where it lingers. In how quietly the structure of behavior begins to loosen.

The food web and trophic cascade of the American alligator in the Florida Everglades.

A System Written Into Temperature

There is another layer to this that does not show itself at the surface.

The structure of that presence is set years earlier, in a place that can be overlooked when standing at the water’s edge. Along the margins of marsh and wetland, slightly above the reach of regular water movement, nests are built from vegetation and sediment, forming mounds that hold heat as they decompose.

Within those mounds, temperature determines something that will not be visible for much later.

Sex is not fixed at fertilization. It emerges during incubation, shaped by the thermal conditions held within the nest. A difference of only a few degrees is enough to shift the outcome, producing more males or more females depending on where within that range the nest remains (Lang & Andrews, 1994; Janzen, 1994).

Under variable conditions—differences in shading, rainfall, timing, and placement—those outcomes are distributed across the landscape. Some nests produce more females, others more males. That variability holds the population in a form that can sustain itself over time.

When conditions become more consistent, that variation narrows.

Warmer nights hold heat longer within the nest. Seasonal transitions extend. The range of outcomes compresses. What was once distributed begins to align.

And that alignment carries forward into the structure of the population—into how individuals occupy space, into how pressure is applied across the system, into what will eventually be visible at the surface.

Alligator eggs hatch after 65 days of incubation in the fall. The babies will chirp to alert their mom, who then digs out the nest while the babies use their egg tooth to hatch from their eggs. Their mom will then safely carry them to the water.

Where the Next Generation Is Set

The placement of those nests depends on something even more constrained.

A narrow band of land that remains above water just long enough to hold them.

That band is not fixed.

It shifts with tide, with rainfall, with the gradual reworking of shoreline that occurs across seasons and years. With rising sea levels, water reaches farther into areas that once remained above it. Flooding becomes more frequent, not always through singular events, but through repeated intrusions that saturate and destabilize what had previously held (Joanen & McNease, 1989; Sweet et al., 2022).

Human alteration compresses this space further.

Hardened shorelines, dredging, and development reduce the gradual transition between land and water. Where there was once a slope capable of holding multiple elevations, there becomes a defined edge. That edge does not provide the same range of conditions required for successful nesting.

The number of suitable sites decreases.

More importantly, the variability between them narrows.

And with that, the system loses one of the mechanisms that allowed it to absorb change.

Alligator on her nest that can hold up to 60 eggs. | Photo credit: National Park Service (NPS)

What Its Presence Means

When an alligator becomes visible along the surface, it reflects conditions that have aligned across multiple layers.

Temperature has reached a range that supports activity. Prey has moved into positions where access becomes possible. Behavioral pressure remains in place across the system. Reproduction has held across enough years, in enough suitable places, to sustain what is now present.

What is seen at the surface is not separate from them.

It is supported by them.

Seeing one does not signal that something has entered the water.

It signals that enough of what lies beneath it—movement, pressure, response, and continuity—remains intact.

And that—even when most of it is not visible—the system is still holding together.

And that is what becomes visible—just long enough to be seen, before the system closes back over it again.

The system does not end at the water’s edge.

Epilogue: Chicken Nugget

We came across him along the New River, near the courthouse in Jacksonville.

We were there to clear what had been left behind—fishing line caught along the walkways, hooks, and the overflow from a trash can that had spilled out onto the edge. Fast food containers, grocery store chicken trays, scattered along the bank. The signs were clear enough. People had been there for a while—crabbing, fishing, eating, leaving what remained.

He was directly below us.

Small enough to miss at first. Still enough to blend into the water until you stopped looking for movement and started noticing what held its position.

A juvenile alligator, watching.

He stayed there while we worked, then slipped beneath the surface and crossed the small bay. On the opposite side, someone tossed a piece of food into the water. He surfaced almost immediately, took it, and remained.

Waiting.

I came back later and stayed longer.

The pattern repeated. He would disappear until footsteps approached, then return to the same place along the edge. Holding position. Watching. Waiting for something to fall.

No fishermen or crabbers passed through while I was there, but the behavior was consistent with what happens when food becomes predictable. Bait, catch, scraps—anything that can be taken without the cost of searching or pursuing.

Energy, without effort.

It is easy to see something like that and respond to what it looks like in that moment. A small animal. Still. Attentive. Something that feels close enough to interact with.

But what is being shaped there is not just a single interaction.

It is behavior.

A shift away from the conditions that formed it—toward something more efficient, more immediate, and less stable over time. The system that once required movement, patience, and response begins to narrow into expectation.

And expectation changes how an animal uses space.

What happens when that animal is no longer small is not a separate question.

It is the continuation of the same pattern.

Alligators do not forget where food has been easy to obtain. They return to it. They hold in those places. They begin to associate presence—human presence—with opportunity.

What begins as something that feels harmless becomes something that alters how the system functions around it.

Not just for the animal, but for everything that responds to it.

There are instincts at work here that were shaped long before any walkway, any dock, any place where food might be dropped from above. Those instincts are not just about survival in isolation. They are part of how pressure is applied, how movement is shaped, how the system holds.

When those instincts are replaced with something easier, the effect does not remain contained.

It carries outward.

He stayed there while I watched. Returning to the same place. Holding the same position. Waiting for something to fall.

There is a kind of kindness in wanting to give something to an animal like that.

But there is another kind in leaving it as it is.

Not interrupting the conditions that shape it. Not narrowing what it has learned to expect. Not replacing a system built on movement and response with one built on waiting.

Let it remember the water as it is.

And you, only as something that passed through it.

We affectionately named this juvenile alligator in the New River in Jacksonville, NC “Chicken Nugget” for all of the chicken nugget boxes left behind on the walkway from an overflowing trash can. | Photo credit: A. Mitchell

References

Atwood, T. B., Connolly, R. M., Ritchie, E. G., Lovelock, C. E., Heithaus, M. R., Hays, G. C., Fourqurean, J. W., & Macreadie, P. I. (2015). Predators help protect carbon stocks in blue carbon ecosystems. Nature Climate Change, 5(12), 1038-1045. https://doi.org/10.1038/nclimate2763

Estes, J. A., Terbough, J., Brashares, J. S., Power, M. E., Berger, J., Bond, W. J., Carpenter, S. R., Essington, T. E., Holt, R. D., & Wardle, D. A. (2011). Trophic Downgrading of Planet Earth. Science, 333(604), 301-306. https://www.science.org/doi/abs/10.1126/science.1205106

Fujisaki, I., Hart, K. M., Mazzotti, F. J., Cherkiss, M. S., Sartain, A. R., Jeffery, B. M., Beauchamp, J. S., & Denton, M. (2014). Home range and movements of American alligators (Alligator mississippiensis) in an Estuary habitat. Animal Biotelemetry, 2(1), 8. https://doi.org/10.1186/2050-3385-2-8

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

Janzen, F. J. (1994). Climate change and temperature-dependent sex determination in reptiles. PNAS, 91(16), 7487-7490. https://doi.org/10.1073/pnas.91.16.7487

Joanen, T., & McNease, L. L. (1989). Ecology and physiology of nesting and early development of the American alligator. American Zoologist, 29(3), 987-998. https://doi.org/10.1093/icb/29.3.987

Lang, J. W., & Andrews, H. V. (1994). Temperature‐dependent sex determination in crocodilians. Journal of Experimental Zoology, 270(1), 28-44. https://doi.org/10.1002/jez.1402700105

Nifong, J. C. (2016). Living on the edge: Trophic ecology of alligator mississippiensis (American alligator) with access to a shallow estuarine impoundment. Bulletin of the Florida Museum of Natural History, 54(2), 13-49. https://doi.org/10.58782/flmnh.xkdw7119

Nifong, J. C., Nifong, R. L., Silliman, B. R., Lowers, R. H., Guillette, L. J., Ferguson, J. M., Welsh, M., Abernathy, K., & Marshall, G. (2014). Animal-borne imaging reveals novel insights into the foraging behaviors and Diel activity of a large-bodied APEX predator, the American alligator (Alligator mississippiensis). PLoS ONE, 9(1), e83953. https://doi.org/10.1371/journal.pone.0083953

Nifong, J. C., & Silliman, B. R. (2013). Impacts of a large-bodied, APEX predator (Alligator mississippiensis Daudin 1801) on salt marsh food webs. Journal of Experimental Marine Biology and Ecology, 440, 185-191. https://doi.org/10.1016/j.jembe.2013.01.002

Ripple, W. J., Estes, J. A., Beschta, R. L., Wilmers, C. C., Ritchie, E. G., Hebblewhite, M., Berger, J., Elmhagen, B., Letnic, M., Nelson, M. P., Schmitz, O. J., Smith, D. W., Wallach, A. D., & Wirsing, A. J. (2014). Status and ecological effects of the world’s largest carnivores. Science, 343(6167). https://doi.org/10.1126/science.1241484

Rosenblatt, A. E., & Heithaus, M. R. (2011). Does variation in movement tactics and trophic interactions among American alligators create habitat linkages? Journal of Animal Ecology, 80(4), 786-798. https://doi.org/10.1111/j.1365-2656.2011.01830.x

Sweet, W. V., Hamlington, B. D., Kopp, R. E., Weaver, C. P., Barnard, P. L., Bekaert, D., Brooks, W., Craghan, M., Dusek, G., Frederickse, T., Garner, G., Genz, A. S., Krasting, J. P., Larour, E., Marcy, D., Marra, J. J., Obeysekera, J., Osler, M., Pendleton, M., … Zuzak, C. (2022). Global and regional sea level rise scenarios for the United States: Updated mean projections and extreme water level probabilities along U.S. coastlines (Technical Report NOS 01). National Oceanic and Atmospheric Administration, National Ocean Service. https://earth.gov/sealevel/us/internal_resources/756/noaa-nos-techrpt01-global-regional-SLR-scenarios-US.pdf

April 3, 2026