Sharks of Onslow County

Tag: coastal ecology

  • How Sharks, Rays, and Ghost Sharks Read an Invisible Ocean

    How Sharks, Rays, and Ghost Sharks Read an Invisible Ocean

    A shadow moves beneath the surface.

    At first, it is only a darker shape inside darker water. Then the shape shifts, and the human mind does what it always does. It tries to make sense of what the eyes are seeing.

    Fish? Ray? Shark? Something else?

    We look harder. We search for a fin, a tail, a clear outline, some familiar clue that lets us name the animal before it disappears again. That is how we enter the ocean. We enter it as visual animals.

    We rely on sight first.

    On land, that makes sense. We look both ways before crossing a street. We recognize faces. We read signs. We notice color, distance, motion, and shape. Even when our other senses help us understand the world, sight usually leads the way.

    But the ocean is not built for human sight.

    Light bends and scatters. Sand clouds the water. Storms stir sediment. Tannins darken creeks and estuaries. Waves break the surface into fragments. A fish can vanish into shadow. A ray can disappear beneath one thin layer of sand. A shark can move through water we are staring directly into and still be almost impossible to see.

    To us, the ocean often becomes less clear the moment we step into it.

    To sharks, rays, skates, sawfish, and chimaeras, that same water is not empty. It is not silent. It is not blank.

    It is filled with signals.

    These animals belong to a group called chondrichthyans, fishes with skeletons made of cartilage instead of bone. Sharks, rays, skates, sawfish, and chimaeras all belong here. We often separate them by the way they look: sharks with their familiar fins and teeth, rays flattened against the bottom, skates moving quietly over sand, sawfish carrying a toothed rostrum, and chimaeras drifting through deeper water like something half-remembered from another age.

    But they are connected by more than cartilage.

    They share sensory worlds that are difficult for us to imagine because they include abilities we do not have in the same way. They use sight, smell, hearing, touch, and temperature, but they also read movement through the water with the lateral line. They detect weak electrical fields with ampullae of Lorenzini. They interpret the ocean through pressure, vibration, chemistry, contrast, motion, and life itself (Collin, 2012; Hart & Collin, 2015).

    We may look into murky water and see almost nothing.

    They may be reading an entire landscape.

    The Ocean as a Different Kind of World

    Sometimes, we do sense the world in ways that remind us we are not only visual.

    A storm approaches, and some people feel pressure before the first drop of rain falls. Sinuses tighten. Migraines build. The air feels different. We walk into a dark room and suddenly sound becomes more important. A creak in the corner, a moving shadow, or a change in the air near our skin, these matter.

    We still try to confirm everything with sight, but when sight weakens, the rest of the body steps forward.

    Now imagine living in a world where sight is helpful, but never enough.

    Water carries information differently than air. A fish swimming does not simply move from one place to another. It pushes water aside. A tailbeat sends movement outward. A struggling animal leaves a different pattern than a calm one. A crab moving under sand may be hidden from view, but its body is still alive. Muscles contract. A heart beats. Nerves fire. Gills pump. Chemicals dissolve and drift.

    Every animal changes the water around it.

    For chondrichthyans, that matters.

    A shark does not have to wait until prey forms a perfect picture in front of its eyes. A ray does not need the seafloor to look busy in order for it to be busy. A skate does not need color to know the bottom is alive. A sawfish does not carry its rostrum only as a weapon. A chimaera in deep water does not move through darkness without information.

    Their sensory systems allow them to gather information across different distances and conditions. Smell, hearing, vision, lateral line detection, and electroreception do not work as separate switches. They overlap, reinforce, and sometimes compensate for one another depending on habitat, prey, visibility, and behavior (Gardiner et al., 2014; Hart & Collin, 2015).

    Their world is not less detailed than ours.

    It is detailed differently.

    Their world is not less detailed than ours.

    It is detailed differently.

    A Shark’s World

    A shark moving through shallow water can be almost impossible to see until it is already there.

    Its body color may match the shifting bottom. Sunlight breaks over its back. Ripples blur the outline. The water may be green, gray, brown, or blue depending on the tide, weather, and sediment. Even in clear water, the shark can appear as a shadow before it appears as an animal.

    To us, the shark is barely more than a shadow. To the shark, the water is already full of information — movement, pressure, chemistry, and weak electrical signals that help it read the world before sight alone confirms what is there. | Image credit: D. Remmers
    To us, the shark is barely more than a shadow. To the shark, the water is already full of information — movement, pressure, chemistry, and weak electrical signals that help it read the world before sight alone confirms what is there. | Image credit: D. Remmers

    But the shark’s awareness does not begin when our eyes finally notice its shape.

    Long before sight confirms what is nearby, other senses may already be gathering information. A fish moving ahead sends pressure changes through the water. A school changing direction creates a pattern of motion. A wounded or stressed animal moves differently than a calm animal. Muscle contractions and heartbeats create weak electrical fields. Odors move through the water as chemical trails.

    To us, the ocean may look open.

    To a shark, it is full of clues.

    The lateral line runs along the body and head and helps detect movement, vibration, and changes in water flow. It is not vision, but it can reveal that something nearby is moving. It can help an animal sense direction, intensity, and disturbance (Webb, 2023).

    The ampullae of Lorenzini add another layer. These small, jelly-filled pores are concentrated around the head and snout. They detect weak electrical fields produced by living animals. This is especially useful at close range, when prey is hidden, when light is low, or when the final decision about an object must be made (Bellono et al., 2017; Hart & Collin, 2015).

    A hammerhead makes this easier to picture.

    Its wide head may look strange to us, but that shape spreads sensory structures across a broader surface. Moving over the bottom, a hammerhead can sweep its head across the sand. A buried ray may be invisible to human eyes. To the shark, the sand may not be silent at all.

    This is where our imagination reaches its limit.

    We can compare electroreception to the feeling of standing near an electrical charge or sensing the strange energy in the air during an intense lightning storm. But even that comparison is weak. We do not move through the world constantly reading tiny electrical fields from other living bodies.

    Sharks do.

    Their world is not a human picture with extra details added. It is a different kind of picture altogether.

    Sight Still Matters

    Sharks have eyes, and those eyes matter.

    They detect contrast, motion, light, shadow, and shape. Many sharks are well suited for low-light conditions. Some have reflective structures behind the retina that help make better use of dim light. This is part of why shark eyes may appear to glow when light catches them underwater. Vision is one piece of a broader sensory strategy that changes by species, habitat, and ecological role (Collin, 2012; Hart & Collin, 2015). 

    But shark vision is not human vision.

    Humans rely heavily on color. We use it to separate objects, judge ripeness, read warning signs, choose clothing, and notice differences in our surroundings. Sharks appear to rely less on color and more on contrast, brightness, movement, and shape. They only have one type of cone photoreceptor with many rods. This makes them more likely to be color blind or have very limited color discrimination (Hart et al., 2019).

    That does not mean sharks see poorly.

    It means color may not be the priority in their world.

    In water, color disappears with depth and distance. Red fades quickly. Light changes constantly. Suspended particles blur edges. A fish flashing silver, a silhouette against the surface, or a sudden burst of movement may matter more than whether something is red, green, or blue.

    A shark’s visual world may be built more from shadow, contrast, motion, and form than from color.

    This is important when we talk about shark-human encounters. A swimmer, surfer, or splashing person at the surface is not being interpreted through human categories. The shark is not thinking “person.” It is receiving a mixture of signals: movement, vibration, silhouette, chemical traces, electrical fields, contrast, and the surrounding activity of fish or bait.

    Sometimes, those signals may be confusing.

    The phrase “mistaken identity” is often used to explain shark bites, but it should be used carefully. It does not explain every bite. It does not mean sharks are foolish. It does not mean they are unable to tell anything apart. It means that, in some situations, the clues available to the shark may overlap with the clues produced by prey. This is why some human silhouettes at the surface can resemble seal and sea lion prey to a shark, especially when viewed from below and under certain movement conditions (Ryan et al., 2021). 

    We know a version of this ourselves.

    Walk through a dark house at night and hear something move in the corner. Your eyes search for shape. Your ears sharpen. Your body tenses before your mind has enough information. You move closer. Maybe you speak into the darkness. Maybe you reach out with your hand or nudge with your foot.

    Then the light turns on, and the intruder becomes a chair with a jacket over it.

    You were not hunting the chair.

    You were investigating a signal you did not fully understand.

    A shark does not have hands. Its fins move it through the water, but they do not investigate the way our fingers do. Its mouth becomes one of the ways it tests the world. That does not make the animal cruel or mindless. It means its body solves a sensory problem differently than ours does.

    For people, that difference can be dangerous. An investigative bite can still cause serious injury. But it is not the same thing as a shark deciding humans belong on the menu.

    Most of the time, we do not match the full pattern of shark prey.

    We smell different. We move differently. We do not behave like fish, rays, turtles, seals, or other natural prey. But in the wrong place, at the wrong time, with the wrong signals around us, we can become part of a confusing sensory scene.

    This is why swimming near active fishing, bait, chum, or dense schools of baitfish matters. The shark is not being summoned by evil intent. It is following information.

    The ocean is speaking in the language it knows.

    The Ocean as Touch and Sound

    A school of fish turns all at once.

    There is no visible leader. No signal we can see. One moment the school moves in one direction, and the next it shifts like one silver body. Each fish keeps its place without crashing into the others. The turn happens faster than sight alone seems able to explain.

    This is one of the easiest ways to understand the lateral line.

    Fish do not only see their neighbors. They feel the water their neighbors move. Each tailbeat, each change in direction, each surge away from danger creates tiny changes in water motion. Those changes travel across the bodies of nearby fish.

    The lateral line detects those movements.

    This sensory system is found in many fishes, not only sharks and rays. It helps animals orient in currents, avoid obstacles, respond to predators, follow prey, and move together in groups. It turns water into a kind of touch-field. The structure and function of the lateral line vary across fishes, but its role in detecting water motion is central to how aquatic animals interpret movement around them (Webb et al., 2023). 

    In sharks, this sense is closely tied to the way sound and vibration move through water. We often think of hearing as something that happens only through ears, but underwater, the whole body can become part of how an animal detects vibration. The lateral line helps a shark feel nearby water movement across its body, while the inner ear detects sound and orientation. Together, these systems make the shark’s body seem less like a body moving through water and more like an instrument tuned to it (Collin, 2012; Hart & Collin, 2015; Webb, 2023).

    For a shark, this means the ocean is never simply open space.

    It has texture.

    A mullet swimming calmly leaves one kind of disturbance. A frightened fish leaves another. A crab moving across the bottom creates a different pattern than a shrimp flicking backward. Waves break. Boat motors pulse. Rain hits the surface. Feet shuffle through sand. A fish struggles on a line. A school turns.

    Each movement changes the water.

    We might stand at the edge of an inlet and see only ripples. A shark, ray, or skate moving through that same water may sense layers of motion overlapping one another. Some signals fade into background noise. Others stand out.

    A calm fish and a frantic fish do not write the same message.

    Along the Onslow County coast, this matters. Our nearshore waters are not always clear. Wind, tide, storms, suspended sand, tannins from creeks, plankton blooms, and wave energy all change visibility. Animals living here cannot depend on sight alone in a world where the water can cloud overnight.

    A shark does not need a perfect view to know something is moving.

    A ray does not need to see every small animal beneath it to know the bottom is alive.

    A fish in a school does not need to wait for its neighbor to bump into it before turning.

    Water carries the conversation.

    The Hidden Electricity of Living Things

    The sandy bottom can look blank.

    A flat stretch of seafloor may seem empty to us, especially when nothing obvious moves. But beneath that surface may be worms, clams, crabs, shrimp, small fish, or rays. Some are hiding. Some are resting. Some are feeding. Some are waiting for the tide to shift.

    To our eyes, they disappear.

    To an animal with electroreception, hidden does not always mean gone.

    Ampullae of Lorenzini allow sharks, rays, skates, sawfish, and chimaeras to detect weak electrical fields. These fields are extremely small, but they are part of what living bodies produce. Muscles contract. Hearts beat. Nerves fire. In saltwater, and especially at close range, those signals can become useful information (Bellono et al., 2017; Collin, 2012).

    The sand may cover the animal.

    It does not erase it.

    This is especially important for animals that feed along the bottom. A shark searching a flat may combine smell, movement, vision, and electroreception. A ray may use similar signals to locate prey in sediment. A sawfish carries this ability into one of the strangest-looking structures in the sea.

    Electroreception also reminds us that the ocean is not only a visual habitat.

    It is a habitat of fields and traces.

    We are used to thinking an animal is hidden when we cannot see it. But concealment depends on who is looking, and how.

    A crab hidden from a bird may not be hidden from a ray.

    A ray hidden from us may not be hidden from a hammerhead.

    A fish buried beneath sand may still be detectable to a predator passing overhead.

    This does not make the ocean more frightening.

    It makes it more alive.

    A Ray’s World

    A stingray resting in shallow water can vanish beneath a thin covering of sand.

    Only the eyes may remain visible. Sometimes even those are difficult to see. The body becomes part of the bottom: a soft outline, a slight rise, a place where the sand seems smoother than the sand around it.

    To us, a buried ray may feel like a surprise.

    To the ray, the world is still open.

    Its eyes sit high on the body, watching the water above. Its mouth is underneath, positioned for feeding along the bottom. Its spiracles allow water to move across the gills while the animal rests or feeds close to the seafloor. Its lateral line and electrosensory system help detect movement and electrical signals nearby (Bedore et al., 2014; Collin, 2012).

    The ray does not need to see the world exactly as we do.

    It lives in layers.

    Above, there may be predators, shadows, swimmers, boats, birds, and changing light. Below and around it, there may be worms, shrimp, crabs, clams, and small fish hidden in or on the sediment. A ray’s flattened body makes sense in this in-between place. It is shaped for bottom life, but it is not cut off from the water column above it.

    Its eyes are important, but they are not everything.

    Rays can detect contrast, shape, motion, and orientation. Some rays may have stronger color discrimination than sharks. Some also have a reflective layer in the eye, the tapetum lucidum, that helps make better use of dim light (Hart et al., 2019). We often compare this to the eye shine seen in cats and other animals at night.

    But a ray buried in sand is not simply waiting with its eyes.

    It is reading pressure. It is reading smell. It is reading electrical traces from animals moving nearby. It is receiving information through more than one doorway.

    This is why the stingray shuffle matters.

    A stingray spine is not used to chase people. It is a defense. When a ray is stepped on or startled from above, the spine can rise quickly. The injury is real, but the behavior is not personal. The ray is responding to pressure and threat in the only way its body allows.

    A shuffled foot gives warning.

    It tells the hidden animal that something large is moving through the sand and gives it a chance to leave before contact happens.

    That small human behavior recognizes something important: the shallow edge is shared space.

    We may be wading through it.

    The ray may be living in it.

    A Skate’s World

    Skates are often confused with rays.

    From above, the difference may not seem important to a casual observer. Both are flattened. Both move close to the bottom. Both can disappear into the shape and color of the seafloor.

    But skates are not simply stingrays without drama.

    They are their own kind of bottom reader.

    Like rays, skates use sensory systems that help them understand the seafloor without relying only on sight. Their eyes are positioned on top of the body, while the mouth is underneath. Their flattened form allows them to move close to the bottom, where many small animals hide in sand, shell hash, mud, and seagrass.

    A skate moving over the bottom is not only looking.

    It is sampling the landscape through touch, smell, pressure, and electricity.

    This makes the bottom less like a floor and more like a page. Each small animal leaves some sign: a movement, a chemical trace, a disturbance, a weak electrical field, a change in sediment (Bedore et al., 2014).

    Skates remind us that not every chondrichthian is built around speed, teeth, and open-water pursuit. Some are built for patience. Some are built for closeness. Some read the world by staying near the place where water meets sediment.

    Along our coast, that meeting place matters.

    Sand flats, tidal creeks, inlets, oyster edges, and shallow nearshore bottoms are not empty spaces between “real” habitats. They are habitats. They hold the smaller lives that larger animals follow.

    To understand the skate or ray, we have to stop seeing the bottom as blank.

    A Sawfish’s World

    A sawfish looks almost impossible the first time you really consider it.

    It has the flattened body of a ray, but extending from the head is a long, tooth-edged rostrum — the “saw” that gives the animal its name. It looks like a weapon, and it can be used that way. Sawfish can swing the rostrum through schools of fish, stunning or injuring prey. It can also help defend the animal.

    But the saw is not only a blade.

    It is also a sensory surface.

    The rostrum contains electroreceptive organs, ampullae of Lorenzini, that help detect weak electrical signals from nearby animals. In other words, the part of the animal that looks most like a weapon is also part of how it reads the world.

    That changes the way we see it.

    A sawfish is not blindly sweeping through water with a strange tool attached to its face. It is carrying a detector through the habitat ahead of its body. The saw helps locate prey. It helps interpret the space in front of the animal. It turns the water ahead into information (Wueringer et al., 2011; Wueringer, 2012).

    This is different from the way we usually imagine rays and skates sensing the bottom.

    A ray or skate often reads the world close to and beneath its flattened body. Its mouth is underneath. Its eyes look upward. Its sensory systems help it interpret the bottom as it rests, glides, or feeds along the sediment. A sawfish, however, extends part of that sensory world forward. The rostrum projects into the water ahead of the body, giving the animal information about prey before the prey reaches the mouth or passes beneath the disc.

    That changes the animal’s sensory shape.

    A sawfish does not only sense what is under it.

    It can sense what is ahead of it.

    The saw becomes a leading edge of perception. As the animal moves, the rostrum samples the space in front of the body. A fish hidden in murky water, a prey item moving near the bottom, or a school passing just ahead may be detected through electrical signals before the sawfish strikes. The same structure that can stun prey can also help find it (Wueringer et al., 2011; Wueringer, 2012).

    That is what makes the sawfish so fascinating.

    The feature that looks most dramatic to us is not simply for attack or defense. It is part of the animal’s sensory map. It stretches the invisible world forward.

    Smalltooth sawfish were historically found as far north as North Carolina, but today they are generally associated with Florida waters in the United States (NOAA Fisheries, 2025). Seeing one along the Onslow County coast would be unusual. Still, they belong in this story because they show how far the chondrichthian sensory world can go.

    A body part we notice for its shape may be important because of what it senses. 

    The ocean often works that way.

    The feature that looks strange to us may be perfectly sensible in the world where the animal lives.

    A Chimaera’s World

    Far from the beach, beyond the bright shallows and beyond the places most of us will ever swim, chimaeras move through deeper water.

    They are sometimes called ghost sharks, though they are not true sharks. They are relatives within the larger chondrichthian group, with cartilage skeletons and a long evolutionary history. Their bodies seem stitched together from familiar parts in unfamiliar ways: large eyes, winglike fins, smooth skin, and tooth plates instead of the replaceable teeth we associate with many sharks.

    They look like animals from the edge of imagination.

    But their strangeness is not random.

    Many chimaeras live in deep, dim environments where sight has limits. In that world, an animal cannot depend on color and daylight the way we do at the surface. Light fades. Pressure increases the deeper you go. The landscape becomes colder, darker, and harder for human senses to understand.

    A chimaera still has eyes, and those eyes can be large. But like other chondrichthyans, chimaeras also use sensory structures that detect electrical fields. In deep water, where prey may be sparse and visibility limited, the ability to detect life without needing a clear visual image becomes essential (Bottaro et al., 2022).

    A chimaera reminds us that “seeing” does not always mean forming a bright picture.

    Sometimes it means detecting what is alive in darkness.

    That may be the hardest part for us to imagine. We tend to picture the deep sea as emptiness because our senses fail there. But the animals that live there are not moving through emptiness. They are moving through a world shaped by pressure, chemistry, temperature, vibration, faint light, and electrical traces.

    The deep sea is not empty.

    It is written in a language we barely read.

    Reading the Ocean Instead of Fearing the Shadow

    It is easy to turn sharks into symbols.

    Fear does that. So do movies, headlines, and stories told from the shoreline after something frightening happens. A fin becomes a threat. A bite becomes proof of intent. A shadow becomes a monster.

    But the real animal is more interesting than the symbol.

    A shark is not moving through the water thinking like a person. A ray is not buried beneath the sand waiting for a human foot. A skate is not a flat shadow without a story. A sawfish is not only a saw. A chimaera is not only a ghost.

    Each animal is built for a sensory world we do not naturally share.

    That does not mean we ignore risk. Quite the opposite. Understanding these senses helps us behave with more respect in the water. We can avoid swimming near fishing activity, bait, or chum. We can pay attention when baitfish are schooling near shore. We can shuffle our feet in ray habitat. We can remember that murky water changes the way animals rely on different senses. We can stop assuming that clear human intent matters in an animal’s sensory landscape.

    The ocean does not interpret us the way we interpret ourselves.

    We may enter the water as swimmers, surfers, paddlers, anglers, or beachgoers. But to the animals already living there, we are also movement, pressure, chemistry, vibration, shadow, sound, and electricity.

    We are part of the signal.

    That is humbling, and it should be.

    Our world is three-dimensional, but it is still mostly built around what we can see. Their world is three-dimensional too, but it includes layers we barely notice.

    They are not seeing less of the ocean than we are. They are reading more of it differently. And maybe that is the point.

    Standing at the edge of the ocean, we see waves, color, and surface. Beneath that surface, other animals are reading movement, pressure, chemistry, and electrical traces in ways we cannot naturally feel. 

    The shark may not be looking for us.

    The ray may not be hiding from us.

    The fish may not be moving randomly.

    They are reading the ocean.

    We are only beginning to learn the alphabet.

    Standing at the edge of the ocean, we see waves, color, and surface. Beneath that surface, sharks, rays, skates, sawfish, and chimaeras read movement, pressure, chemistry, shadow, and electrical traces in ways we cannot naturally feel. | Image credit: A. Mitchell
    Standing at the edge of the ocean, we see waves, color, and surface. Beneath that surface, sharks, rays, skates, sawfish, and chimaeras read movement, pressure, chemistry, shadow, and electrical traces in ways we cannot naturally feel. | Image credit: A. Mitchell

    References

    Bangley, C. (2026, January 26). Sharks of NC. Coastwatch. https://ncseagrant.ncsu.edu/coastwatch/the-sharks-of-north-carolina/

    Bedore, C. N., Harris, L. L., & Kajiura, S. M. (2014). Behavioral responses of batoid elasmobranchs to prey-simulating electric fields are correlated to peripheral sensory morphology and ecology. Zoology, 117(2), 95-103. https://doi.org/10.1016/j.zool.2013.09.002

    Bellono, N. W., Leitch, D. B., & Julius, D. (2017). Molecular basis of ancestral vertebrate electroreception. Nature, 543(7645), 391-396. https://doi.org/10.1038/nature21401

    Bottaro, M. (2022). Sixth sense in the deep-sea: The electrosensory system in ghost shark Chimaera monstrosa. Scientific Reports, 12(1). https://doi.org/10.1038/s41598-022-14076-2

    Collin, S. P. (2012). The Neuroecology of cartilaginous fishes: Sensory strategies for survival. Brain, Behavior and Evolution, 80(2), 80-96. https://doi.org/10.1159/000339870

    Gardiner, J. M., Atema, J., Hueter, R. E., & Motta, P. J. (2014). Multisensory integration and behavioral plasticity in sharks from different ecological niches. PLoS ONE, 9(4), e93036. https://doi.org/10.1371/journal.pone.0093036

    Hart, N. S., & Collin, S. P. (2015). Sharks senses and shark repellents. Integrative Zoology, 10(1), 38-64. https://doi.org/10.1111/1749-4877.12095

    Hart, N. S., Lamb, T. D., Patel, H. R., Chuah, A., Natoli, R. C., Hudson, N. J., Cutmore, S. C., Davies, W. I., Collin, S. P., & Hunt, D. M. (2019). Visual Opsin diversity in sharks and rays. Molecular Biology and Evolution, 37(3), 811-827. https://doi.org/10.1093/molbev/msz269

    NOAA Fisheries. (2025). Smalltooth sawfish. NOAA. https://www.fisheries.noaa.gov/species/smalltooth-sawfish

    Ryan, L. A., Slip, D. J., Chapuis, L., Collin, S. P., Gennari, E., Hemmi, J. M., How, M. J., Huveneers, C., Peddemors, V. M., Tosetto, L., & Hart, N. S. (2021). A shark’s eye view: Testing the ‘mistaken identity theory’ behind shark bites on humans. Journal of The Royal Society Interface, 18(183). https://doi.org/10.1098/rsif.2021.0533

    Webb, J. F. (2023). Structural and functional evolution of the mechanosensory lateral line system of fishes. The Journal of the Acoustical Society of America, 154(6), 3526-3542. https://doi.org/10.1121/10.0022565

    Wueringer, B. E. (2012). Electroreception in elasmobranchs: Sawfish as a case study. Brain, Behavior and Evolution, 80(2), 97-107. https://doi.org/10.1159/000339873

    Wueringer, B., Peverell, S., Seymour, J., Squire, Jr., L., Kajiura, S., & Collin, S. (2011). Sensory systems in Sawfishes. 1. The ampullae of Lorenzini. Brain, Behavior and Evolution, 78(2), 139-149. https://doi.org/10.1159/000329515

  • The Marsh’s Quiet Workforce: More Than a Rabbit

    The Marsh’s Quiet Workforce: More Than a Rabbit

    More Than Meets the Eye

    Spend enough time walking along a salt marsh and you’ll eventually stop noticing the marsh rabbits.

    Not because they’ve disappeared.

    Because they’ve become part of the landscape.

    They feed quietly along the marsh edge, slipping into the grasses when startled before appearing again somewhere you didn’t expect. Some evenings you may count half a dozen. Other days you wonder if there were ever any there at all.

    Unlike the brighter cottontails many people are used to seeing, marsh rabbits are darker, with coarse brown to reddish-brown fur, a grayish underside, and a rusty cinnamon patch along the back of the neck. Even the tail gives them away. Instead of flashing bright white, it appears darker and more bluish, one reason marsh rabbits have sometimes been called “bluetails” (Chapman & Trani, 2007; Chapman & Willner, 1981).

    Like so much of the marsh, they’re easy to overlook.

    A marsh rabbit may look like a familiar backyard visitor, but its role reaches far beyond the grass beneath it. | Image credit: skylarkymalarkey, iNaturalist
    A marsh rabbit may look like a familiar backyard visitor, but its role reaches far beyond the grass beneath it. | Image credit: skylarkymalarkey, iNaturalist

    For more than a century, naturalists have described marsh rabbits (Sylvilagus palustris) by documenting where they lived, what they looked like, and what they ate (Rhoads & Young, 1897). Those observations gave us our first understanding of the species. Today, ecology invites us to ask a different question.

    What happens because marsh rabbits are here?

    The answer reaches far beyond the rabbit itself.

    We often measure an animal’s importance by how exciting it is to watch.

    The marsh doesn’t.

    The marsh measures importance by how many lives are connected to one another (Soulé et al., 2003).

    Following One Rabbit

    If you’ve ever taken a science class, you’ve probably learned the First Law of Conservation of Energy: energy cannot be created or destroyed. It only changes form.

    For many of us, that idea remained in a textbook or written across a classroom whiteboard. It became something to memorize rather than something we expected to witness.

    Yet every walk beside a salt marsh quietly brings that principle to life.

    Standing beside a marsh, it’s easy to underestimate what you’re seeing. From a distance, much of it appears to be little more than grass. Yet every growing season those grasses capture enormous amounts of energy from the sun, making salt marshes among the most productive ecosystems on Earth (Frizzell, 1988).

    That productivity, however, cannot remain in the plants.

    It has to move.

    Imagine following a single marsh rabbit through its life.

    Following one marsh rabbit means following the grasses, cover, and hidden pathways that connect it to the larger marsh. | Image credit: jorgenols, iNaturalist
    Following one marsh rabbit means following the grasses, cover, and hidden pathways that connect it to the larger marsh. | Image credit: jorgenols, iNaturalist

    At only about 2.5 to 3.5 pounds, its small body holds energy gathered first by the marsh plants around it (Chapman & Trani, 2007; Chapman & Willner, 1981).The grasses it consumes become muscle, bone, blood, fur, and new life. That rabbit may one day feed a hawk, an owl, a fox, a bobcat, or a snake. Throughout its life it supports parasites. After its death it feeds scavengers, fungi, bacteria, and countless decomposers before eventually returning nutrients to the marsh where another season of growth begins.

    Nothing has appeared from nowhere.

    Nothing has truly disappeared.

    The energy has simply changed form.

    Every day, marsh rabbits transform marsh vegetation into something that can support an entirely different community of organisms (Chapman & Trani, 2007; Chapman & Willner, 1981).

    The rabbit isn’t the end of the story.

    In many ways, it’s where the story begins.

    More Than a Meal

    Spend a few minutes watching a marsh rabbit and it may not seem particularly busy.

    It grazes along the marsh edge, pauses to listen, slips into dense cover, then returns to feeding when the danger seems to have passed. At first glance, it looks like a small animal moving through its day.

    But even before a marsh rabbit becomes food for something else, it is already shaping the marsh around it.

    Every bite influences which plants are grazed and which continue growing (Conner & Cherry, 2017). As it moves between the marsh edge, nearby cover, and slightly higher ground, the rabbit is also moving through the boundary between habitats most of us see as separate. The same dense vegetation that protects the rabbit also provides shelter for insects, reptiles, amphibians, birds, and countless other small lives moving through the marsh (Canepuccia et al., 2023; Larsen & Gray et al., 2021; Wigley & Lancia, 1998).

    A marsh rabbit browses at the edge, where each ordinary bite helps move energy through the landscape. | Image credit: cadecampbell, iNaturalist
    A marsh rabbit browses at the edge, where each ordinary bite helps move energy through the landscape. | Image credit: cadecampbell, iNaturalist

    This is why the rabbit matters before the hawk ever appears.

    Its value is not limited to becoming prey. Its ordinary life helps move energy, shape vegetation, and connect habitats long before that energy travels farther up the food web (Chapman & Trani, 2007; Chapman & Willner, 1981; Conner & Cherry, 2017).

    Perhaps that is the quiet work of a marsh rabbit.

    Not simply feeding something else.

    But helping hold together the conditions that allow so much else to live there.

    Why There Are So Many

    Sometimes marsh rabbits seem to be everywhere — in yards, along road edges, near parking lots, and wherever the Spartina meets slightly higher ground.

    A young marsh rabbit beside an adult shows the visible side of abundance, but reproduction is only part of the story. | Image credit: Wolfgang, iNaturalist
    A young marsh rabbit beside an adult shows the visible side of abundance, but reproduction is only part of the story. | Image credit: Wolfgang, iNaturalist

    The easy explanation is that rabbits reproduce quickly. They can produce several litters in a year, often three to seven, with roughly 15 to 20 young produced annually under favorable conditions (Holler & Conaway, 1979). 

    That is true, but it is not the whole story.

    Nature rarely invests heavily in something that does not matter. In a marsh, abundance is not waste. It is part of the system. 

    Marsh rabbits live under constant pressure. Every choice — where to feed, when to move, when to freeze, and when to disappear into the grasses — is shaped by predators, tides, weather, and the daily balance between finding food and becoming food (Hill et al., 2019; Holler & Conaway, 1979).

    Predators influence far more than the animals they catch. Their presence can change where prey feed, how long they remain exposed, and how energy moves through the landscape (Suraci et al., 2019). When predator communities shift, those changes can ripple through the food web in ways that affect many other species (Bransford et al., 2024; Jiménez et al., 2019) .

    Seen this way, abundant marsh rabbits are not simply evidence of successful reproduction.

    They are evidence of how much work this one ordinary species performs.

    The Rabbit You Didn’t See

    Perhaps this also explains something you’ve probably noticed yourself. 

    One moment several marsh rabbits are feeding along the marsh edge.

    You look away for only a moment.

    When you look back, they’re gone.

    They haven’t left the marsh.

    Unlike many rabbits people are used to seeing, marsh rabbits are strong swimmers. Water is not simply something they avoid; it is part of the landscape they know how to use. In a place shaped by tides, wet ground, and narrow edges of cover, the ability to move through water helps explain how they can vanish so completely without ever leaving the marsh (Chapman & Trani, 2007; Chapman & Willner, 1981). 

    The same dense vegetation that feeds them also protects them. Slight changes in elevation, the rhythm of the tides, the angle of the evening sun, and generations of natural selection have shaped an animal that survives by knowing exactly when to be seen — and when not to be (Chapman & Willner, 1981; Holler & Conaway, 1979).

    The rabbit disappeared from sight.

    Its place in the marsh never did.

    Looking at the Marsh Differently

    The next time you notice a marsh rabbit quietly feeding along the marsh edge, pause before it disappears.

    What once looked like an ordinary rabbit is now something entirely different.

    Not because the rabbit has changed.

    But because you can now see the countless connections passing through it (Soulé et al., 2003).

    And once you see those connections, the marsh becomes harder to overlook.

    A marsh rabbit slips back into the edge, leaving only a glimpse of the connections still moving through the marsh. | Image credit: maxnel, iNaturalist
    A marsh rabbit slips back into the edge, leaving only a glimpse of the connections still moving through the marsh. | Image credit: maxnel, iNaturalist

    References

    Bransford, T. D., Harris, S. A., & Forys, E. A. (2024). Seasonal variation in mammalian Mesopredator spatiotemporal overlap on a barrier island complex. Animals, 14(16), 2431. https://doi.org/10.3390/ani14162431

    Canepuccia, A. D., Fanjul, M. S., & Iribarne, O. O. (2023). Global distribution and richness of terrestrial mammals in tidal marshes. Diversity and Distributions, 29(5), 598-612. https://doi.org/10.1111/ddi.13683

    Chapman, B. R., & Trani, M. K. (2007). Marsh Rabbit (Sylvilagus palustris). In The Land Manager’s Guide to Mammals of the South (pp. 247-251). Durham, NC: The Nature Conservancy; Atlanta, GA: U.S. Forest Service.

    Chapman, J. A., & Willner, G. R. (1981). Sylvilagus palustris. Mammalian Species, (153), 1. https://doi.org/10.2307/3503947

    Conner, L. M., & Cherry, M. J. (2017). Considering Herbivory and Predation in Forest Management. In Ecological Restoration and Management of Longleaf Pine Forests (1st ed., p. 12). CRC Press.

    Frizzell, E. K. (1988). Mammals and Wetlands. In The Ecology and Management of Wetlands: Volume 1: Ecology of Wetlands (1st ed., pp. 213-226). Croom Helm Ltd.; Timber Press.

    Hill, J. E., DeVault, T. L., & Belant, J. L. (2019). Cause‐specific mortality of the world’s terrestrial vertebrates. Global Ecology and Biogeography, 28(5), 680-689. https://doi.org/10.1111/geb.12881

    Holler, N. R., & Conaway, C. H. (1979). Reproduction of the marsh rabbit (Sylvilagus palustris) in South Florida. Journal of Mammalogy, 60(4), 769-777. https://doi.org/10.2307/1380192

    Jiménez, J., Nuñez-Arjona, J. C., Mougeot, F., Ferreras, P., González, L. M., García-Domínguez, F., Muñoz-Igualada, J., Palacios, M. J., Pla, S., Rueda, C., Villaespesa, F., Nájera, F., Palomares, F., & López-Bao, J. V. (2019). Restoring APEX predators can reduce mesopredator abundances. Biological Conservation, 238, 108234. https://doi.org/10.1016/j.biocon.2019.108234

    Larsen-Gray, A. L., Loeb, S. C., & Kalcounis-Rueppell, M. C. (2021). Rodent population and community responses to experimental, large scale, long-term coarse Woody debris manipulations. Forest Ecology and Management, 496, 119427. https://doi.org/10.1016/j.foreco.2021.119427

    Macarthur, R., & Levins, R. (1967). The limiting similarity, convergence, and divergence of coexisting species. The American Naturalist, 101(921), 377-385. https://doi.org/10.1086/282505

    Rhoads, S. N., & Young, R. T. (1897). Notes on a Collection of Small Mammals from Northeastern North Carolina. Proceedings of the Academy of Natural Sciences of Philadelphia, 49, 303-312. https://www.jstor.org/stable/4062279?seq=1

    Soulé, M. E., Estes, J. A., Berger, J., & Del Rio, C. M. (2003). Ecological effectiveness: Conservation goals for interactive species. Conservation Biology, 17(5), 1238-1250. https://doi.org/10.1046/j.1523-1739.2003.01599.x

    Suraci, J. P., Clinchy, M., Zanette, L. Y., & Wilmers, C. C. (2019). Fear of humans as APEX predators has landscape‐scale impacts from mountain lions to mice. Ecology Letters, 22(10), 1578-1586. https://doi.org/10.1111/ele.13344

    Wigley, T. B., & Lancia, R. A. (1998). Wildlife Communities. In Southern Forested Wetlands (1st ed., p. 32). Routledge.

  • Where the Sand Breathes: Life Beneath the Tide Line in Onslow County

    Where the Sand Breathes: Life Beneath the Tide Line in Onslow County

    Most beachgoers look across the shoreline and see a boundary.

    The ocean ends. The land begins.

    But the strip of sand where waves wash ashore and slide back toward the sea is not really either one. It is a threshold—a place that becomes ocean and land again with every passing wave.

    At first glance, this narrow band of wet sand appears empty. There are no marsh grasses, no oyster reefs, and no obvious schools of fish. Yet beneath the surface, the sand is alive with animals digging, filtering, feeding, hunting, and breathing.

    This is the swash zone: the constantly shifting seam between ocean and land.

    It is one of the most overlooked ecosystems on the North Carolina coast.

    The swash zone is the narrow strip of shoreline where waves wash ashore and then retreat back toward the sea. Though it may appear to be little more than wet sand, it supports a diverse community of animals adapted to life between ocean and land. | Image credit: J. Morales
    The swash zone is the narrow strip of shoreline where waves wash ashore and then retreat back toward the sea. Though it may appear to be little more than wet sand, it supports a diverse community of animals adapted to life between ocean and land. | Image credit: J. Morales

    The Beach That Never Stops Moving

    Unlike a marsh, oyster reef, or seagrass meadow, the swash zone never stays still.

    Each wave pushes seawater into the sand and then pulls it back out again. Water moves through the spaces between sand grains, carrying oxygen, microscopic algae, bacteria, and organic matter. The sand itself acts almost like a living filter, supporting communities of organisms adapted to conditions that change minute by minute (Brown & McLachlan, 2018; McLachlan & Defeo, 2018).

    To survive here, animals must tolerate burial, shifting sediments, crashing waves, changing salinity, and predators arriving from both land and sea.

    Few species can endure such instability.

    Those that do are specialists (Defeo et al., 2009).

    The Living Wave Riders: Mole Crabs and Coquina Clams

    If you’ve ever noticed the wet sand suddenly shimmer or seem to move as a wave retreats, you’ve likely witnessed two of the swash zone’s most abundant residents.

    Atlantic Mole Crabs (Emerita talpoida)

    An Atlantic mole crab, in Surf City, NC, briefly exposed at the surface of the swash zone. Within seconds, these specialized crustaceans can bury themselves beneath the sand, where they spend most of their lives filtering food from the surf. | Image credit: johnnybirder, iNaturalist
    An Atlantic mole crab, in Surf City, NC, briefly exposed at the surface of the swash zone. Within seconds, these specialized crustaceans can bury themselves beneath the sand, where they spend most of their lives filtering food from the surf. | Image credit: johnnybirder, iNaturalist

    Known locally as sand fleas, Atlantic mole crabs spend nearly their entire lives buried beneath the surface of the swash zone.

    They are not true crabs. Instead, they belong to a group of highly specialized crustaceans adapted for life where waves break on the shore. Their bodies are smooth, streamlined, and shaped almost like a small bean. Using powerful rear legs, they can bury themselves in saturated sand in seconds (Abude et al., 2024).

    When waves wash overhead, they extend feathery antennae into the water and filter microscopic plankton and organic particles from the surf (Abude et al., 2024).

    Rather than remaining stationary, mole crabs occupy the constantly shifting swash zone, where food and oxygen are delivered by breaking waves. Their abundance makes them one of the most important food sources for shorebirds, fish, and ghost crabs (Abude et al., 2024).

    Coquina Clams (Donax variabilis)

    Sharing the same habitat is one of the most recognizable shells on Atlantic beaches.

    Coquina clams are the tiny, brightly colored shells scattered across the tide line in shades of pink, yellow, purple, blue, orange, and white.

    Most people only notice the shells.

    The living animal beneath them is remarkably adapted to life in moving sand.

    Coquinas live just beneath the surface of the swash zone where they filter microscopic algae and suspended particles from the water. As waves advance and retreat, they repeatedly rebury themselves, using a muscular foot to dig into the sand with astonishing speed (Ellers, 1995).

    Like mole crabs, coquinas are adapted to the dynamic conditions of the swash zone. Their abundance provides food for fish, crabs, and shorebirds, making them a critical link between microscopic plankton and larger coastal predators (Wilson, 1999).

    Standing at the water’s edge, it is easy to think the beach is motionless.

    In reality, thousands of coquinas and mole crabs may be moving beneath your feet with every wave.

    The Night Shift: Atlantic Ghost Crabs (Ocypode quadrata)

    Higher on the beach, above the reach of most waves, another resident waits.

    Atlantic ghost crabs spend daylight hours hidden inside deep burrows excavated into the sand. Their pale coloration blends almost perfectly with the beach, making them difficult to see unless they move.

    Atlantic ghost crabs spend daylight hours hidden in burrows above the tide line. Their pale coloration provides excellent camouflage against the sand, making them surprisingly difficult to spot until they move. | Image credit: A. Mitchell
    Atlantic ghost crabs spend daylight hours hidden in burrows above the tide line. Their pale coloration provides excellent camouflage against the sand, making them surprisingly difficult to spot until they move. | Image credit: A. Mitchell

    While the swash zone below is dominated by animals filtering food from the surf, ghost crabs are hunters and scavengers.

    After sunset, they emerge to patrol the shoreline, feeding on mole crabs, coquina clams, stranded marine organisms, insects, carrion, and whatever other opportunities the beach provides (Wolcott, 1978).

    Many beachgoers never see them at all. Instead, they notice the evidence they leave behind. Round burrow openings dot the upper beach. Fresh tracks crisscross the sand overnight and disappear with the next tide. Occasionally, a pale shape darts sideways through the beam of a flashlight before vanishing into darkness.

    Those burrows tell a story of their own. Beaches with abundant ghost crab burrows often support richer communities of animals living both above and below the sand, which is why scientists sometimes use ghost crabs as one way of assessing beach condition and disturbance (Schlacher et al., 2016).

    The next time you notice a round hole in the upper beach with a pile of freshly excavated sand nearby, you are likely looking at the entrance to a ghost crab burrow—and evidence that the beach is still very much alive after dark.

    Between the Grains

    The largest residents of the swash zone are only part of the story.

    Beneath the surface lies an even larger community that most beachgoers never see. Between individual grains of sand are tiny water-filled spaces that form a hidden habitat known as the interstitial zone. To us, a handful of wet sand looks solid. To these organisms, it is an underwater landscape of tunnels, chambers, and passageways (Higgins & Thiel, 1988).

    The beach is layered with hidden communities. From amphipods and ghost crabs higher on the shore to coquina clams and mole crabs at the water's edge, different species occupy distinct zones shaped by waves, moisture, food availability, and shifting sand. | Image credit: Michel et al., 2016
    The beach is layered with hidden communities. From amphipods and ghost crabs higher on the shore to coquina clams and mole crabs at the water’s edge, different species occupy distinct zones shaped by waves, moisture, food availability, and shifting sand. | Image credit: Michel et al., 2016

    Amphipods: The Cleanup Crew

    The line of seaweed, shells, and debris left behind by the tide may look messy, but it is often one of the busiest places on the beach.

    Hidden among the wrack, in the upper intertidal zone, are amphipods, small crustaceans often called Atlantic beach hoppers (Americorchestia longicornis). If you sift through a pile of damp seaweed or drift algae, you may catch a glimpse of them springing away before disappearing back into cover.

    Much of what washes ashore eventually becomes food for something else. Amphipods feed on decaying seaweed, dead animals, and other organic material stranded by the tide. In doing so, they help break down material that would otherwise accumulate along the shoreline. They also become food themselves, supporting shorebirds, fish, and other invertebrates that forage along the beach (Dugan et al., 2003).

    Polychaete Worms: Engineers Beneath the Sand

    Most beachgoers never see the worms living beneath the tide line, but their work is happening constantly beneath the surface.

    As polychaete worms burrow through the sand, they create tiny pathways that allow water and oxygen to penetrate deeper into the sediment. In many ways, they perform the same role that earthworms do in a garden, except their garden is the beach itself.

    Some species spend their lives feeding on organic material trapped between the sand grains, such as Lugworms (Arenicolidae). Others hunt small crustaceans and worms moving through the sediment such as Bloodworms (Glyceridae) and Paddle Worms / Shimmy Worms (Nephtyidae). As they burrow, feed, and move through the beach, they continually mix the sand and help create conditions that allow countless other organisms to survive there (McLachlan & Defeo, 2018).

    Ribbon Worms: Hidden Predators

    Not every animal beneath the sand is feeding on algae, bacteria, or decaying material.

    Ribbon worms (Nemertea) are predators, though few people ever realize they are there. Hidden beneath the surface, they hunt some of the same tiny animals that share the spaces between the sand grains, including small worms, crustaceans, and other invertebrates moving through the sediment (Thiel & Kruse, 2001).

    Many possess a remarkable feeding structure called a proboscis that can be rapidly extended to capture prey (Thiel & Kruse, 2001).

    Most beachgoers will never see a ribbon worm, yet they are part of the same hidden food web as the amphipods, copepods, and nematodes surrounding them. Even beneath a seemingly empty stretch of sand, animals are feeding, avoiding predators, and competing for resources every hour of the day.

    Nematodes: Life at Microscopic Scale

    If you could shrink yourself down and explore a handful of wet sand, the landscape would look very different.

    What appears solid to us is actually filled with tiny spaces between the grains. Moving through those water-filled passages are microscopic animals called nematodes (phylum Nematoda).

    These tiny roundworms feed on bacteria, algae, fungi, and organic matter coating the sand. Though nearly invisible, they are among the most abundant animals on many beaches and play an important role in breaking down organic material and recycling nutrients throughout the sediment (Coull, 1999; Schratzberger & Ingels, 2018).

    Harpacticoid Copepods: Tiny Links in the Food Web

    Sharing those same microscopic spaces are harpacticoid copepods (Paraleptastacus wilsoni), tiny crustaceans that spend their lives moving between individual sand grains.

    They graze on algae and microbial films coating the sediment, feeding on resources too small for larger animals to use directly. In turn, they become prey for larger invertebrates and juvenile fishes.

    Most beachgoers will never see a harpacticoid copepod. Yet every handful of wet sand may contain a community of animals like these, quietly connecting the microscopic world to the larger food web of the beach (Schratzberger & Ingels, 2018).

    Individually, these animals are easy to overlook.

    Collectively, they form much of the living foundation of the tide line. The coquinas, mole crabs, ghost crabs, fishes, and shorebirds visible along the shoreline all depend, directly or indirectly, on countless small interactions taking place beneath the sand.

    Following the Birds

    One of the easiest ways to observe this hidden ecosystem is not by looking down.

    It is by looking up.Anyone who spends time on the beach has likely watched sanderlings (Calidris alba) racing along the edge of the surf. They dart forward as a wave retreats, stop suddenly to probe the sand, and then sprint away from the next incoming wave. A little farther up the beach, ruddy turnstones (Arenaria interpres) pick through wrack lines left behind by the tide. Along the surf edge, Eastern willets (Tringa semipalmata semipalmata) walk deliberately through the shallows, searching for movement beneath the water.

    To many beachgoers, they are simply birds feeding along the shoreline.

    What they are actually doing is reading the beach.

    Each probe into the sand is a search for prey hidden beneath the surface. Mole crabs, small worms, amphipods, coquinas, and other invertebrates living within the tide line provide food for these birds (Dugan et al., 2003; Hubbard & Dugan, 2003).

    The birds go where the food is.

    When shorebirds gather along a stretch of beach, they are often revealing an ecosystem that would otherwise remain invisible. Their presence tells us that the sand beneath them is alive with prey, even if we cannot see it ourselves. 

    In many ways, shorebirds act as interpreters of the tide line. By watching where they feed, pause, and congregate, we gain a glimpse into the hidden community supporting them below.

    Reading the Beach

    From a distance, the tide line can seem almost empty. A narrow strip of wet sand separates the ocean from the rest of the beach. Waves arrive, waves leave, and little appears to change.

    Spend a few minutes watching, however, and a different picture begins to emerge.

    Shorebirds gather where the surf is most active. Tiny shells appear and disappear with the retreating waves. Fresh ghost crab burrows punctuate the upper beach. Even the wrack line left behind by the tide becomes a gathering place for scavengers and foraging birds.

    What first appears to be a simple boundary between land and sea begins to look more like a busy shoreline neighborhood.

    At first glance, the tide line can appear almost empty. Look a little longer, however, and the clues begin to emerge—feeding shorebirds, scattered shells, and the constant movement of the surf all hint at the hidden community living beneath the sand. | Image credit: A. Mitchell
    At first glance, the tide line can appear almost empty. Look a little longer, however, and the clues begin to emerge—feeding shorebirds, scattered shells, and the constant movement of the surf all hint at the hidden community living beneath the sand. | Image credit: A. Mitchell

    The animals living here are responding to the same thing: the constant movement of the tide. Food arrives with the surf, becomes available for a brief moment, and is quickly claimed by whatever creature is best adapted to find it. Some filter it from the water. Some collect it from the sand. Others hunt the animals already feeding there.

    Because these organisms live so closely tied to the conditions of the beach, changes in their numbers can provide clues about the habitat itself (Defeo et al., 2009). A shoreline where birds are feeding, ghost crab burrows remain active, and life continues to reveal itself at the edge of the surf is often a sign that this narrow strip of beach is supporting the community that depends upon it.

    When those communities decline, the change may not be immediately obvious. Yet over time the beach can begin to feel quieter. Fewer birds stop to feed. Fewer burrows appear in the sand. The signs become harder to find. Those changes can ripple outward through the food web, affecting species both on the beach and beyond it (Peterson et al., 2006).

    The Threshold

    The next time you stand at the edge of the surf, watch where the waves pause before sliding back toward the sea.

    It is easy to see this narrow strip of shoreline as a boundary. Ocean on one side. Land on the other.

    But the tide line is not really a dividing line at all.

    It is a place where both worlds meet.

    With every passing wave, food, oxygen, and life arrive from the ocean. Beneath the sand, animals capture it, consume it, recycle it, and pass it on. Shorebirds search for it. Ghost crabs emerge after dark to hunt it. Countless organisms spend their entire lives within a space that is neither fully ocean nor fully land.

    Most people walk across this strip of beach without ever noticing it.

    Yet it is one of the busiest places along the coast.

    The next time you see shells appearing and disappearing in the surf, a flock of sanderlings racing the tide, or ghost crab burrows scattered across the upper beach, remember that these are not separate observations. They are pieces of the same story.

    What appears to be an empty stretch of wet sand is actually a living threshold—a place where ocean and land remain connected through countless interactions happening beneath every step.

    And once you see it, it becomes difficult to look at the shoreline the same way again.

    The tide line in Surf City, NC may appear to be little more than wet sand. Yet beneath every retreating wave lies a hidden community connecting ocean and land through countless interactions, most of them unseen. | Image credit: A. Mitchell
    The tide line in Surf City, NC may appear to be little more than wet sand. Yet beneath every retreating wave lies a hidden community connecting ocean and land through countless interactions, most of them unseen. | Image credit: A. Mitchell

    References

    Abude, R. R., Lôbo-Hajdu, G., Moreira, D. A., & Cabrini, T. M. (2024). Sandy beach mole crabs (Decapoda: Hippidae: Emerita): A systematic review of the anthropic impacts, populations density, and conservation strategies. Marine Environmental Research, 202, 106745. https://doi.org/10.1016/j.marenvres.2024.106745

    Coull, B. C. (1999). Role of meiofauna in estuarine soft‐bottom habitats. Australian Journal of Ecology, 24(4), 327-343. https://doi.org/10.1046/j.1442-9993.1999.00979.x

    Defeo, O., McLachlan, A., Schoeman, D. S., Schlacher, T. A., Dugan, J., Jones, A., Lastra, M., & Scapini, F. (2009). Threats to sandy beach ecosystems: A review. Estuarine, Coastal and Shelf Science, 81(1), 1-12. https://doi.org/10.1016/j.ecss.2008.09.022

    Dugan, J. E., Hubbard, D. M., McCrary, M. D., & Pierson, M. O. (2003). The response of macrofauna communities and shorebirds to macrophyte wrack subsidies on exposed sandy beaches of Southern California. Estuarine, Coastal and Shelf Science, 58, 25-40. https://doi.org/10.1016/s0272-7714(03)00045-3

    Ellers, O. (1995). Behavioral control of swash-riding in the clam Donax variabilis. The Biological Bulletin, 189(2), 120-127. https://doi.org/10.2307/1542462

    Hubbard, D. M., & Dugan, J. E. (2003). Shorebird use of an exposed sandy beach in Southern California. Estuarine, Coastal and Shelf Science, 58, 41-54. https://doi.org/10.1016/s0272-7714(03)00048-9

    McLachlan, A., & Defeo, O. (2018). The ecology of sandy shores (3rd ed.). Academic Press.

    P, H. R., & Thiel, H. (1988). Intro study meiofauna. Smithsonian Books (DC).

    Peterson, C. H., Bishop, M. J., Johnson, G. A., D’Anna, L. M., & Manning, L. M. (2006). Exploiting beach filling as an unaffordable experiment: Benthic intertidal impacts propagating upwards to shorebirds. Journal of Experimental Marine Biology and Ecology, 338(2), 205-221. https://doi.org/10.1016/j.jembe.2006.06.021

    Pilkey, O. H., Rice, T. M., & Neal, W. J. (2014). How to read a North Carolina beach: Bubble holes, Barking sands, and rippled Runnels. UNC Press Books.

    Schlacher, T. A., Lucrezi, S., Connolly, R. M., Peterson, C. H., Gilby, B. L., Maslo, B., Olds, A. D., Walker, S. J., Leon, J. X., Huijbers, C. M., Weston, M. A., Turra, A., Hyndes, G. A., Holt, R. A., & Schoeman, D. S. (2016). Human threats to sandy beaches: A meta-analysis of ghost crabs illustrates global anthropogenic impacts. Estuarine, Coastal and Shelf Science, 169, 56-73. https://doi.org/10.1016/j.ecss.2015.11.025

    Schratzberger, M., & Ingels, J. (2018). Meiofauna matters: The roles of meiofauna in benthic ecosystems. Journal of Experimental Marine Biology and Ecology, 502, 12-25. https://doi.org/10.1016/j.jembe.2017.01.007

    Thiel, M., & Kruse, I. (2001). Status of the nemertea as predators in marine ecosystems. Hydrobiologia, 456(1-3), 21-32. https://doi.org/10.1023/a:1013005814145

    Wilson, J. G. (1999). Population dynamics and energy budget for a population of Donax variabilis (Say) on an exposed South Carolina beach. Journal of Experimental Marine Biology and Ecology, 239(1), 61-83. https://doi.org/10.1016/s0022-0981(99)00027-1

    Wolcott, T. G. (1978). Ecological role of ghost crabs, Ocypode quadrata (Fabricius) on an ocean beach: Scavengers or predators? Journal of Experimental Marine Biology and Ecology, 31(1), 67-82. https://doi.org/10.1016/0022-0981(78)90137-5

  • The Fish That Follows the Tide: American Eels Along the Waters of Onslow County

    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 life cycle of the American eel along the waters of Onslow County 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
    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
    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
    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
    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
    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
    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
    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
    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

  • Where Wings Meet Water: Reading Birds Along the Edges of Onslow County

    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
    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
    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

  • Threshold Species at the Year’s Turn

    Threshold Species at the Year’s Turn

    Winter birds and hidden skates in a changing coastal system

    Late December along the coast does not announce itself loudly. The holidays have passed, the shoreline empties, and the light—almost imperceptibly—begins to return. The winter solstice marks the shortest day of the year, but its ecological counterpart is quieter. The water does not reset. It settles.

    This is the moment when the coastal ecosystem stops negotiating with the season and begins to accept it. That acceptance is visible, if you know where to look—above the waterline in the form of a small diving duck, and below the surface in the stillness of a benthic predator that does not announce its presence at all.

    In our region, ecologists recognize certain animals as threshold species: species whose presence, or subtle change in behavior, signals that the system has crossed a seasonal threshold in energy, behavior, and stability — moving from late year into what comes next.

    Above the Water: When Winter Is No Longer a Question

    Male (left) and female (right) Bufflehead ducks enjoying a winter swim | Photo credit: Judy Gallagher, iNaturalist

    By late December, one species begins to appear with quiet regularity across protected sounds and estuaries: the Bufflehead (Bucephala albeola).

    Buffleheads are not early winter arrivals. They do not surge in during the first cold fronts of autumn, nor do they linger indecisively during seasonal transition. Instead, their presence reflects commitment. By the time buffleheads settle into coastal waters, water temperatures have stabilized at winter lows, turbulence has eased in protected areas, and benthic prey communities—particularly small crustaceans and mollusks—have shifted into predictable winter distributions (Eadie et al., 2000; Goudie et al., 1994).

    Ecologically, buffleheads are specialists. They forage by diving, relying on clear water and reliable prey patches. Their winter distribution is shaped not by calendar dates but by energy economics: cold water increases metabolic demands, and winter habitats must reliably repay that cost (Eadie & Kehoe, 2022). Where buffleheads remain, the system has crossed a threshold from fluctuation to stability.

    In this way, they function less as migrants and more as indicators. Their presence signals that the coastal year has finished rearranging itself. Winter has arrived—not dramatically, but decisively.

    Below the Water: When Stillness Makes Life Visible

    Clearnose skate in winter waters | Photo credit: NOAA Fisheries

    Below the surface, the signal is subtler.

    Skates do not arrive in winter with the clarity of birds overhead. Species such as the Clearnose skate (Rostroraja eglanteria) are present along the southeastern U.S. coast throughout much of the year. What changes in late December is not their location, but their visibility.

    As water temperatures drop, skates reduce activity, conserving energy through decreased movement and prolonged periods of resting on the seafloor (Di Santo & Bennett, 2011). This metabolic slowdown coincides with seasonal increases in water clarity driven by reduced biological productivity, lower sediment resuspension, and diminished boat traffic (Cloern et al., 2014). The result is a paradox: winter reveals what summer conceals.

    In these conditions, skates become easier to observe—not because they have increased in number, but because the system itself has slowed enough to make persistence visible. Their flattened bodies blend seamlessly into sandy or muddy substrates, a strategy optimized for ambush predation and energy conservation rather than movement (Carrier et al., 2012).

    If buffleheads announce that winter has settled, skates confirm it. They represent endurance over motion, patience over migration.

    The Ecological Hinge Between Years

    Neither of these species marks a beginning. Neither signals renewal or arrival in the way spring migrants do. Instead, they occupy the hinge between years—the moment when the ecosystem accepts the constraints of winter and reorganizes around them.

    Late December is not biologically empty. It is a period of recalibration. Energy budgets tighten. Movements become deliberate. Survival depends less on abundance than on efficiency.

    Above the water, buffleheads gather where the math works. Below it, skates persist by minimizing expenditure altogether. One is easily seen, the other almost never. Together, they reveal the same truth: the system has crossed a line.

    After the Turn

    January will bring its own changes. Cold will deepen, or ease. Migratory patterns will sharpen. New signals will emerge. But the moment just after the solstice—just after the holidays—is different. It is when the coast pauses, holds, and commits.

    The year does not turn loudly here.
    It settles, and then it holds.

    References

    Carrier, J. C., Musick, J. A., & Heithaus, M. R. (2012). Biology of sharks and their relatives (2nd ed.). CRC Press. https://doi.org/10.1201/b11867 

    Cloern, J. E., Foster, S. Q., & Kleckner, A. E. (2014). Phytoplankton primary production in the world’s estuarine–coastal ecosystems. Biogeosciences, 11(9), 2477–2501. https://doi.org/10.5194/bg-11-2477-2014 

    Di Santo, V., & Bennett, W. A. (2011). Is post-feeding thermotaxis advantageous in elasmobranch fishes? Journal of Fish Biology, 78(7), 1950–1965. https://doi.org/10.1111/j.1095-8649.2011.02976.x 

    Eadie, J. M., & Kehoe, F. P. (2022). Energetics and foraging ecology of diving ducks. In P. G. Rodewald (Ed.), The birds of North America. Cornell Lab of Ornithology.
    https://doi.org/10.2173/bna 

    Eadie, J. M., Savard, J. P. L., & Mallory, M. L. (2000). Barrow’s Goldeneye (Bucephala islandica) and Bufflehead (Bucephala albeola). In A. Poole & F. Gill (Eds.), The birds of North America. Cornell Lab of Ornithology. https://doi.org/10.2173/bna.548 

    Goudie, R. I., Brault, S., Conant, B., Kondratyev, A. V., Petersen, M. R., & Vermeer, K. (1994). The status of sea ducks in the North Pacific Rim: Toward their conservation. Transactions of the North American Wildlife and Natural Resources Conference, 59, 27–49. https://pubs.usgs.gov/publication/70187692