Sharks of Onslow County

Category: Marine Ecosystem

  • When the Water Feels Different: What Warmer Summers Mean Along the Onslow County Coast

    When the Water Feels Different: What Warmer Summers Mean Along the Onslow County Coast

    Most changes in the ocean happen long before we notice them.

    The water still looks blue. Waves continue to break across the sandbars. Beachgoers spread their towels beneath the same summer sun, children chase ghost crabs along the tide line, and anglers cast into the surf hoping for a bite.

    Yet beneath the surface, a warming ocean is altering the conditions that shape life along the coast.

    The changes begin with microscopic organisms drifting through the water column and ripple outward through fish, shellfish, jellyfish, and eventually the people who swim, fish, and play in these waters. Scientists have documented rising ocean temperatures worldwide, with the ocean absorbing the vast majority of the excess heat generated by a warming climate (IPCC, 2023; NASA, 2025).

    For beachgoers along the Onslow County coast, these changes often appear as small observations. Water that feels warmer than it once did. Green swirls visible in drone photographs. Jellyfish gathering along the shoreline. Questions about bacteria, shellfish closures, and changing fish patterns.

    At first glance, these may seem unrelated.

    In reality, they are all connected.

    A Longer Summer Beneath the Surface

    The ocean does not warm as quickly as the air above it, but it holds heat much longer.

    As coastal waters warm earlier in spring and remain warm later into autumn, marine organisms experience something similar to a longer growing season on land. Processes that once occurred over a few summer months may now persist for much longer periods – lasting later into the year or shifting the timing of organisms that are responding to environmental conditions (IPCC, 2023; Menzel et al., 2006).

    For marine life, temperature influences nearly everything. Growth rates, feeding behavior, reproduction, migration, and metabolism are all affected by the warmth of the surrounding water (Pörtner & Knust, 2007).

    For many species, warmer water means increased biological activity. But every response carries consequences that ripple through the food web.

    The first organisms to respond are often the smallest.

    When Tiny Things Respond First

    Most beachgoers never think about what is suspended in the water around them.

    Unlike a forest, marsh, or coral reef, much of the ocean’s life is not immediately visible. Looking across the surf, the water may appear empty except for an occasional fish, jellyfish, or diving bird.

    Yet the water column itself is home to countless drifting organisms. Some are microscopic plants. Others are microscopic animals. Together, they form a community known as plankton.

    Among the most important are phytoplankton—tiny plant-like organisms that drift with currents and tides. Though nearly invisible to the naked eye, they capture sunlight, form the foundation of marine food webs, and produce much of the oxygen found in Earth’s atmosphere (Falkowski et al., 1998).

    Feeding on them are zooplankton, a diverse group of drifting animals that includes tiny crustaceans, larval fish, and the early life stages of many marine organisms. Nearly everything in the ocean depends on this microscopic world in some way.

    As temperatures rise and sunlight remains abundant, phytoplankton growth can increase. In many cases, this increased productivity benefits marine ecosystems by providing more food for zooplankton, shellfish, and small fish.

    Sometimes, however, the changes become visible.

    Drone photographs, fishing reports, and satellite imagery occasionally reveal ribbons and swirls of green water along the coastline. Many people assume these colors indicate pollution, but the explanation is often more complex.

    In some cases, the green color reflects increased concentrations of phytoplankton. In others, it may result from suspended sediment, river discharge, or other naturally occurring materials in the water (Behrenfeld et al., 2006).

    Green water does not automatically mean unhealthy water.

    More often, it is a visible reminder that biological activity is taking place beneath the surface—activity that most beachgoers never see.

    In fact, many periods of greener water reflect productive conditions that support marine food webs. Increased phytoplankton can provide more food for zooplankton, shellfish, and small fish, creating benefits that ripple through the ecosystem. The presence of abundant microscopic life is often a sign that the ocean is actively supporting the organisms that depend upon it.

    Not all blooms are beneficial, however.

    Occasionally, beachgoers hear news reports about harmful algal blooms and wonder whether the water they are seeing is part of one.

    Under certain conditions, a small number of phytoplankton species can reproduce so rapidly that they begin affecting the ecosystem around them. These events are known as harmful algal blooms.

    Along U.S. coastlines, some of the better-known examples include Karenia brevis, which causes many Gulf Coast red tides; Alexandrium species, which can produce toxins associated with paralytic shellfish poisoning; and Pseudo-nitzschia, which produces domoic acid and has been linked to shellfish closures and wildlife impacts in several regions (Anderson et al., 2012; Trainer et al., 2012).

    Unlike the seasonal increases in phytoplankton that help support marine food webs, harmful blooms can stress marine life and create concerns for people. Some produce toxins that accumulate in shellfish, leading to temporary harvesting closures. Others contribute to oxygen declines as large concentrations of algae die and decompose (Anderson et al., 2002).

    For beachgoers, the challenge is that harmful blooms do not always look the way people expect. A bloom may appear as a patch of unusually dense water, a streak of discoloration, or sometimes little different from surrounding water. Color alone rarely tells the whole story. 

    In some cases, blooms may discolor the water, turning it red, rust-colored, brown, orange, or an unusually dense green. Some may also produce odors that people describe as sulfur-like, fishy, or similar to decaying vegetation (Gilbert et al., 2005; Gobler, 2020).

    Not all green water is the same. Satellite imagery can reveal differences in phytoplankton concentrations across coastal waters. Many blooms support productive marine ecosystems, while others may become dense enough to affect water quality and ecosystem health. | Image credit: EPA cyanWeb, https://qed.epa.gov/cyanweb/
    Not all green water is the same. Satellite imagery can reveal differences in phytoplankton concentrations across coastal waters. Many blooms support productive marine ecosystems, while others may become dense enough to affect water quality and ecosystem health. | Image credit: EPA cyanWeb, https://qed.epa.gov/cyanweb/

    Fortunately, most periods of pale green, emerald green, or slightly tea-colored water along the Carolina coast are not harmful algal blooms. More often, they reflect normal concentrations of phytoplankton, suspended sediment, river discharge, or other natural processes.

    The challenge is that the water does not always reveal which is which at first glance. What appears to be a simple color change may be telling a much more complicated story beneath the surface.

    The Oxygen Paradox

    Warm water creates a biological contradiction.

    As temperatures rise, marine organisms require more oxygen to stay active and carry out basic life processes. At the same time, warmer water naturally holds less dissolved oxygen—the tiny oxygen molecules mixed into the water that fish, crabs, and many other marine animals breathe. Unlike oxygen in the air around us, this oxygen must remain suspended within the water itself, and warmer water cannot hold as much of it as cooler water (Keeling et al., 2010).

    In other words, as the demand for oxygen increases, the supply decreases. Scientists refer to this growing challenge as ocean deoxygenation, a phenomenon driven in part by warming oceans and documented in coastal waters around the world (Breitburg et al., 2018; Diaz & Rosenberg, 2008).

    The effects are often invisible to beachgoers. Unlike a jellyfish bloom or a patch of green water, low oxygen leaves few obvious clues for someone standing on the shoreline. 

    Fish may become sluggish, gather near inlets or channels, or disappear from places where they are normally common long before any obvious signs appear at the surface. Crabs, shrimp, and other marine organisms must work harder to find places with enough oxygen to survive. Some may move into shallower water, concentrate in tidal channels, or bury themselves in sediment where conditions remain tolerable. Some areas become less favorable, while others provide temporary pockets of suitable habitat.

    The ocean begins to rearrange itself.

    Following the Fish

    Stand on the beach long enough and patterns begin to emerge.

    A stretch of water that looked empty an hour ago suddenly flickers with baitfish. Birds gather over a patch of surf. A school of fish appears just beyond a sandbar, then vanishes as quickly as it arrived.

    Most of these movements happen without drawing much attention. To someone walking the shoreline, the ocean can seem unchanged from one day to the next.

    Beneath the surface, however, marine life is constantly adjusting.

    Fish are not fixed to one place. They move through the water searching for conditions that suit them, often responding to changes that people cannot see. A slight difference in temperature, a pocket of water with more oxygen, or a concentration of prey can be enough to shift where fish gather (Pörtner & Knust, 2007).

    Along the beaches of Onslow County, these adjustments may be playing out right in front of us.

    Anglers sometimes notice schools of mullet, menhaden, silversides, or other baitfish stacked along a sandbar. Predatory fish such as bluefish, Spanish mackerel, red drum, or even small sharks may linger near an inlet. Feeding activity may suddenly erupt close to shore, with baitfish leaping from the water as predators chase them, birds diving repeatedly into the surf, and flashes of silver visible just beyond the breakers. Tides, currents, and seasonal migrations all help shape these patterns, but fish are also responding to the changing conditions around them.

    Even the breaking surf can matter.

    Where waves tumble across shallow bars, the water is constantly being mixed and stirred. Oxygen from the atmosphere is worked back into the water, creating conditions with higher oxygen levels than nearby areas where the water is calmer and moves less. What looks like nothing more than a line of breaking waves can become a place where marine life gathers.

    Most beachgoers never notice these subtle shifts.

    They simply see fish where fish happen to be.

    Yet changing ocean conditions are becoming an increasingly important part of the story. Fish may feed in a different stretch of surf than usual, baitfish may gather in unexpected places, or seasonal arrivals may occur a little earlier or later than expected. Most of the time, the reasons remain hidden beneath the surface, but the movements themselves reveal that marine life is responding to a changing ocean (Pinsky et al., 2013).

    The ocean is not standing still.

    And neither are the fish.

    The Species That Thrive

    Not every organism responds to warming water in the same way.

    Some struggle.

    Others thrive.

    For many beachgoers, one of the most noticeable signs of seasonal change arrives as translucent shapes drifting through the surf. As plankton populations increase and warm conditions persist, the same environmental changes influencing fish and other marine life can also create favorable conditions for jellyfish. 

    Jellyfish are a familiar part of coastal life in Onslow County, but their numbers can vary dramatically from season to season. During late spring, summer, and early fall, when air and water temperatures commonly reach about 68–86°F (20–30°C), conditions often become more favorable for larger jellyfish populations than during the colder months.

    Most people first notice them while wading in the shallows, scanning the water from a pier, or walking the beach after a storm. A shoreline that seemed empty a few weeks earlier may suddenly hold dozens of stranded jellyfish along the tide line. Depending on the season, visitors might encounter moon jellies pulsing just beneath the surface, cannonball jellies washing ashore in clusters, or the unmistakable blue floats of Portuguese man o’ war carried in by winds and currents.

    A shoreline covered with cannonball jellies can appear almost overnight. In reality, the conditions supporting these blooms often develop over weeks or months as water temperatures, food availability, and ocean currents change. | Image credit: Cape Hatteras National Seashore
    A shoreline covered with cannonball jellies can appear almost overnight. In reality, the conditions supporting these blooms often develop over weeks or months as water temperatures, food availability, and ocean currents change. | Image credit: Cape Hatteras National Seashore

    These appearances can feel sudden, but they rarely are.

    A shoreline that seems free of jellyfish one week may be dotted with them the next. To someone standing on the beach, it can feel as though they arrived overnight.

    Much of a jellyfish’s life unfolds out of sight. Many drift offshore, while others pass through life stages that most people never notice. As waters warm and food becomes more abundant, conditions can support larger populations. Sometimes the result is a bloom—a period when unusually large numbers gather in coastal waters and become difficult to ignore.

    In reality, the conditions that support them may have been developing for weeks or even months. While warmer water does not automatically mean more jellyfish everywhere (Condon et al., 2012), seasonal warming can contribute to periods when jellyfish become unusually abundant in nearshore waters. Currents, food availability, and other environmental factors also influence when and where these blooms occur (Purcell, 2005; Richardson et al., 2009).

    For observers on the shore, jellyfish are often among the first visible reminders that changes in ocean conditions do not stay hidden beneath the surface for long.

    Not every organism has the ability to drift or swim away.

    The Organisms That Cannot Leave

    Fish can relocate.

    Jellyfish can drift with currents.

    Shellfish remain where they are.

    For many beachgoers, oysters, clams, and mussels are simply part of the coastal landscape—something encountered at low tide, served at a seafood restaurant, or harvested during shellfish season.

    Yet these animals spend their lives doing something remarkable.

    Oysters, clams, mussels, and other shellfish continuously draw water through their bodies, removing microscopic food particles as they feed. This is why they are known as filter feeders. A single adult oyster can filter up to 50 gallons (190 L) of water per day, depending on temperature, salinity, and other environmental factors (Jansen, 2023; zu Ermgassen et al., 2012).

    An oyster reef does not simply sit on the bottom. Day and night, every oyster is quietly filtering the estuary around it. 

    Because they process so much water, shellfish become closely connected to the conditions around them. Changes in temperature, oxygen levels, harmful algal blooms, and water quality can all affect their health and survival (Shumway, 1990).

    For this reason, shellfish often serve as some of the earliest indicators that environmental conditions have changed. 

    When shellfish harvesting areas are temporarily closed, many people assume pollution is the only explanation. In reality, closures may occur for a variety of reasons, including elevated levels of bacteria such as fecal coliforms, Escherichia coli (E. coli), or Enterococcus, harmful algal blooms, or other conditions that could affect human health (Food & Drug Administration (FDA), 2023).

    In many cases, these closures are evidence that monitoring programs are working exactly as intended.

    The shellfish are not causing the problem.

    They are revealing it.

    By filtering the surrounding water day after day, they provide a glimpse into conditions that might otherwise go unnoticed.

    Sometimes, what they reveal is a bacterium that has received increasing attention in recent years.

    The Bacteria That Was Already Here

    Few marine organisms have generated more public concern in recent summers than Vibrio bacteria.

    News headlines often make it sound like a new arrival.

    It is not.

    Like the phytoplankton, zooplankton, and countless other organisms drifting through coastal waters, Vibrio vulnificus has always been part of the hidden community beneath the surface.

    Most beachgoers never notice it. They cannot see it. They do not think about it while wading through the surf or collecting shells along the shoreline.

    Yet these bacteria have long occupied an important ecological role.

    Vibrio species occur naturally in coastal and estuarine waters around the world. They help break down organic matter and recycle nutrients, returning materials to the food web where they can be used again by other organisms. If they were somehow eradicated, scientists would expect dead plants, algae, fish, and other organic material to break down more slowly. Over time, beach wrack could linger longer along shorelines, decaying material could accumulate in marshes and tidal flats, and nutrients normally returned to the water and sediment would become less available to the organisms that depend on them. These changes might not be obvious at first, but they could gradually alter the health and productivity of coastal ecosystems (Oliver, 2005).

    The organic material accumulating along a wrack line supports a hidden community of decomposers. Among them are naturally occurring bacteria that help recycle nutrients and keep coastal ecosystems functioning. Image credit: S. Hilldebrand, U. S. Fish and Wildlife Service
    The organic material accumulating along a wrack line supports a hidden community of decomposers. Among them are naturally occurring bacteria that help recycle nutrients and keep coastal ecosystems functioning. Image credit: S. Hilldebrand, U. S. Fish and Wildlife Service

    What often changes first is not the presence of these organisms, but their abundance.

    Just as warmer conditions can influence phytoplankton growth, they can also affect microbial communities.

    Most of the time, these changes remain invisible.

    The water may look the same. The beach may feel the same. Nothing about a morning walk along the shoreline suggests that microscopic populations are shifting beneath the surface.

    Yet they are.

    When water temperatures rise well above the normal seasonal range for a region and remain elevated for extended periods, conditions can become more favorable for certain Vibrio species. Their populations may increase, raising the likelihood of human exposure (Baker-Austin et al., 2012; Baker-Austin et al., 2018).

    For most healthy beachgoers, swimming in coastal waters remains a normal part of enjoying the beach.

    However, individuals with open wounds, compromised immune systems, or underlying health conditions may face greater risks and should pay closer attention to local advisories and public health guidance.

    The story is not really about a dangerous bacterium suddenly appearing where it did not belong.

    It is another example of a broader pattern that runs throughout coastal ecosystems.

    As environmental conditions change, the organisms already living there respond. Some become more abundant. Others become less common. Together, their responses reveal something easy to miss while standing at the water’s edge: the shoreline is alive with countless forms of life that most of us never see.

    Even the smallest inhabitants are connected to the larger changes unfolding around them.

    Reading the Signs

    Most beachgoers will never measure dissolved oxygen or monitor water temperatures.

    What they will notice are the signs: water that stays warm later into autumn, green swirls visible from a fishing pier or drone photograph, jellyfish gathering along a tide line, fish appearing in unexpected places, temporary shellfish closures, or questions about bacteria that have long existed in coastal waters.

    None of these observations tells the whole story on its own.

    Taken together, however, they reveal an ecosystem responding to warmer conditions one species, one season, and one degree at a time.

    Looking Beneath the Surface

    Most changes in the ocean begin out of sight.

    Long before beachgoers notice a jellyfish drifting through the surf or a patch of green water offshore, microscopic organisms are already responding to changing conditions. Fish adjust their movements. Oxygen levels shift. Shellfish filter whatever the water brings.

    By the time we notice the signs, the ecosystem has often been responding for weeks or months.

    The water may feel the same as it always has beneath our feet. Yet each summer offers new clues about the changes taking place below the surface—if we know where to look.

    The ocean often appears unchanged from one day to the next. Beneath the surface, however, countless organisms are responding to shifting temperatures, oxygen levels, food availability, and water quality. The more we learn to observe, the more the shoreline reveals. | Image credit: A. Mitchell
    The ocean often appears unchanged from one day to the next. Beneath the surface, however, countless organisms are responding to shifting temperatures, oxygen levels, food availability, and water quality. The more we learn to observe, the more the shoreline reveals. | Image credit: A. Mitchell

    References

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    Anderson, D. M., Glibert, P. M., & Burkholder, J. M. (2002). Harmful algal blooms and eutrophication: Nutrient sources, composition, and consequences. Estuaries, 25(4), 704-726. https://doi.org/10.1007/bf02804901

    Baker-Austin, C., Oliver, J. D., Alam, M., Ali, A., Waldor, M. K., Qadri, F., & Martinez-Urtaza, J. (2018). Vibrio spp. infections. Nature Reviews Disease Primers, 4(1), 1-9. https://www.nature.com/articles/s41572-018-0005-8

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  • 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

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  • The Life of a Barnacle

    The Life of a Barnacle

    A microscopic epic of drift, decision, and devotion

    On a winter walk along a pier in Surf City, the boards are bleached pale by sun and salt. Wind threads through the pilings. Gulls cry over gray water. At your feet, on a beam that has known decades of tides, something clings.

    It is no bigger than a fingernail—chalky white, ridged like a tiny volcano. Along this coast, it is often an ivory barnacle—Amphibalanus eburneus—one of the small architects that quietly carpet pilings, docks, and seawalls from Topsail Sound to the Cape Fear. You could scrape it away with the edge of a shell. You probably have, absentmindedly, a hundred times.

    But this barnacle is not debris. It is a biography written in calcium.

    It began as a drifting dot—an invisible life in a moving sea. It crossed currents. It tasted the chemistry of places. And then, once, it chose.

    The choice was final.

    Barnacles are among the few animals on Earth that get exactly one chance to decide where they will live. No revisions. No migrations. No second homes. The place where a barnacle settles becomes the place where it will eat, grow, reproduce, and die. Its entire life collapses into a single coordinate on the map of the shore.

    To understand a barnacle is to understand what it means to commit.

    Ivory barnacles cling to a rock | Photo credit: Ken-ichi Ueda
    Ivory barnacles cling to a rock | Photo credit: Ken-ichi Ueda

    Drift

    A barnacle’s life begins in motion.

    After fertilization, barnacle embryos hatch into nauplius larvae—tiny, triangular forms equipped with beating appendages and a simple eye (Anderson, 1994). They rise into the plankton, where they may drift for days to weeks, feeding and growing as tides and currents carry them outward (Chen et al., 2014).

    The first larval stage of a barnacle, called a nauplius, is free-swimming and distinguished by a set of "horns." | Photo credit: Robert Bachand
    The first larval stage of a barnacle, called a nauplius, is free-swimming and distinguished by a set of “horns.” | Photo credit: Robert Bachand

    They are not aimless. Even at this scale, nauplii respond to light, salinity, and gravity. They migrate vertically through the water column, riding layers of current like conveyor belts. Their world is vast and borderless—and lethal.

    Most barnacles die here.

    Nauplii are eaten by copepods, jellyfish, fish larvae, and filter-feeding invertebrates. Each pulse of water is a gauntlet. Survival depends on number: millions released so that a few may reach shore.

    After several molts, the nauplius enters its final larval form: the cyprid.

    A late larval barnacle stage, the cypris, has a bivalved shell of chitin and glands in its first antennae that are used to cement itself permanently to a hard substrate. | Photo credit: Robert Bachand
    A late larval barnacle stage, the cyprid, has a bivalved shell of chitin and glands in its first antennae that are used to cement itself permanently to a hard substrate. | Photo credit: Robert Bachand

    This is no longer a feeding animal. It is a vessel of stored energy, built for a single task—finding a place to live (Aldred & Clare, 2008).

    The cyprid does not eat.

    A clock begins.

    Much of what we know about this hidden stage comes from decades of work on a close coastal relative, the striped barnacle – Amphibalanus amphitrite—a warm-water barnacle that clings to pilings and boat hulls worldwide, and whose larvae have become a window into how barnacles read the sea.

    The striped barnacle (Amphibalanus amphitrite) is a globally distributed, non-native barnacle species that can spread via biofouling. In North Carolina waters it may occur outside its historical native range, but it isn’t widely recognized as a documented invasive species causing major ecological disruption. | Photo Credit: South Australia Marine Lab
    The striped barnacle (Amphibalanus amphitrite) is a globally distributed, non-native barnacle species that can spread via biofouling. In North Carolina waters it may occur outside its historical native range, but it isn’t widely recognized as a documented invasive species causing major ecological disruption. | Photo Credit: South Australia Marine Lab

    The Narrow Window

    Now the barnacle is no longer drifting blindly. It swims with intent. The cyprid probes surfaces with specialized antennules, “tasting” the chemistry of rock, wood, shell, and steel. It detects microbial biofilms—thin living skins that signal a surface has been stable long enough to support life (Qian et al., 2007). It senses the presence of other barnacles. It avoids surfaces that feel wrong.

    This sensory world evolved in seas that were chemically simpler.

    Today, cyprids swim through waters laced with heavy metals, hydrocarbons, microplastics, antifouling compounds, and nutrient-driven microbial shifts. These pollutants alter biofilms, mask settlement cues, and interfere with larval sensory systems. What once read clearly as “home” now arrives as static.

    In degraded waters, cyprids often hesitate. They probe and retreat. They circle without committing.

    But the clock does not pause.

    Depending on species and temperature, a cyprid has only days to a few weeks before its stored energy is exhausted (Aldred & Clare, 2008). Each hour of searching burns fuel. When reserves fall too low, three futures unfold.

    Some larvae simply die in the plankton and sink.

    Some make a desperate choice—cementing themselves to marginal or unstable surfaces.

    Others respond to distorted cues and settle where survival is unlikely.

    This is not a failure of instinct. It is a mismatch between ancient sensory logic and a changed sea.

    Long before we notice a shoreline growing quieter, its future has already thinned in the plankton.

    In the life of a barnacle, adverse intergenerational effects of microplastics might drastically reduce larval recruitment and threaten long-term zooplankton sustainability. | Photo credit: Yu & Chan, 2020.
    Adverse intergenerational effects of microplastics might drastically reduce larval recruitment and threaten long-term zooplankton sustainability. | Photo credit: Yu & Chan, 2020.

    The Choice

    When the answer is yes, the barnacle performs one of the most irreversible acts in the animal kingdom.

    It flips upside down.

    Using its antennules, the cyprid secretes a permanent biological cement and glues its head to the surface (Kamino, 2016). This adhesive—among the strongest natural glues known—binds underwater to stone, metal, and polymer. Once cured, it cannot be undone.

    There is no “testing.” No trial period.

    This is the end of motion.

    Within hours, the cyprid undergoes a radical metamorphosis. Its eyes degenerate. Its swimming limbs are restructured into feathery feeding appendages called cirri. Its body reorganizes around a new axis—rooted instead of free (Høeg & Møller, 2006).

    The barnacle becomes architecture.

    Many do not survive even this. Newly settled juveniles are grazed by small fish and invertebrates. Waves scrape them away before cement fully cures. The shoreline is littered with choices that did not last.

    Those that remain begin to build something larger than themselves.

    A Life Built Around the Tide

    Most animals grow by addition. Barnacles grow by reinvention.

    Shell plates rise around soft tissue, forming a fortress against wave impact, desiccation, and predation. Inside, muscles and organs reorganize to support a life of rhythmic feeding.

    When submerged, the barnacle opens its opercular plates and unfurls its cirri—six pairs of jointed limbs that sweep the water in steady arcs. Each beat captures phytoplankton, detritus, and microcrustaceans (Southward, 2008).

    An ivory barnacle (Amphibalanus eburneus) unfurls its cirri that sweep the water to feed. | © Peter J. Bryant
    An ivory barnacle (Amphibalanus eburneus) unfurls its cirri that sweep the water to feed. | © Peter J. Bryant

    Metabolism slows. Heat and salt concentrate. Time folds inward. Some intertidal barnacles endure body temperatures exceeding 40°C (104°F) and prolonged oxygen deprivation (Harley, 2008). They wait for the sea to return.

    Each tide is both a threat and nourishment.

    Anatomy of a barnacle. | Photo Credit: AnimalFact.com
    Anatomy of a barnacle. | Photo Credit: AnimalFact.com

    Time in Shell

    Barnacles record time the way trees do.

    Their shells grow in increments, forming visible growth bands that reflect seasonal cycles and environmental stress (Crisp, 1989). Storms leave signatures. Cold winters slow deposition. Productive summers thicken walls.

    A barnacle on a piling may live five, ten, even twenty years (Southward, 2008). It will experience thousands of tides, hundreds of storms, and uncountable shifts in salinity and temperature—without ever moving.

    Where foraminifera archive ancient seas in sediment, barnacles archive living shorelines in calcium.

    They are clocks that cannot leave.

    Looking at the head of the barnacle, where it attaches, growth rings can be seen. These concentric rings that represent cyclic growth periods are called ecdysal lines (also known as cuticular slips) and are associated with barnacle molting. | Photo credit: © Michael Ready Photography
    Looking at the head of the barnacle, where it attaches, growth rings can be seen. These concentric rings that represent cyclic growth periods are called ecdysal lines (also known as cuticular slips) and are associated with barnacle molting. | Photo credit: © Michael Ready Photography

    Threshold Organisms

    Barnacles occupy one of the most punishing habitats on Earth: the intertidal zone.

    Here, organisms must withstand:

    • Wave forces exceeding hurricane winds
    • Repeated drying and rehydration
    • Rapid temperature swings
    • Salinity changes from rain and evaporation
    • Intense ultraviolet exposure

    Few animals can survive here. Barnacles not only survive—they structure the place.

    Every barnacle on this shore is the consequence of a single larval decision made weeks earlier in open water.

    They stabilize surfaces. They retain moisture. They create crevices for algae, worms, snails, and juvenile crustaceans. They shape temperature gradients and water flow. They turn bare rock into habitat.

    When settlement falters—when larvae cannot read the shore or run out of time—the architecture of the coast changes.

    Bare rock expands. Algal communities shift. Grazers lose shelter. Predators lose prey. The intertidal simplifies.

    A piling with fewer barnacles is not merely cleaner. It is quieter. Biologically poorer and less layered.

    The Lesson in Shell

    Return now to that single barnacle on the pier.

    It has no eyes. It has never seen the ocean. It will never know the gull overhead or the human who pauses above it. And yet it has shaped its entire existence around this exact sliver of coast.

    It did not choose perfectly.

    Some barnacles settle too high and starve. Some attach where sand scours them away. Some cement themselves beside competitors that outgrow and smother them.

    There is no guarantee.

    Only the act of choosing.

    In a world that prizes movement, flexibility, and endless revision, the barnacle offers a quieter philosophy:

    At some point, life must become a place.

    To belong is not to drift forever. It is to accept exposure. To endure storms. To open when the tide allows. To grow, layer by layer, into the shape of your ground.

    Every barnacle on this coast is a monument to a single irreversible decision.

    And the sea is full of them.

    Bay barnacle, Amphibalanus improvisus, on a rock in the New River | Photo credit: Alina Michele, iNaturalist, 2022
    Bay barnacle, Amphibalanus improvisus, on a rock in the New River | Photo credit: Alina Michele, iNaturalist, 2022

    References

    Aldred, N., & Clare, A. S. (2008). The adhesive strategies of cyprids and development of barnacle-resistant marine coatings. Biofouling, 24(5), 351-363. https://doi.org/10.1080/08927010802256117

    Anderson, D. T. (1994). Barnacles: Structure, function, development and evolution (1st ed.). Springer Dordrecht.

    Chen, Z., Zhang, H., Wang, H., Matsumura, K., Wong, Y. H., Ravasi, T., & Qian, P. (2014). Quantitative Proteomics study of larval settlement in the barnacle balanus Amphitrite. PLoS ONE, 9(2), e88744. https://doi.org/10.1371/journal.pone.0088744

    Crisp, D. J. (1989). Tidally deposited bands in shells of barnacles and molluscs. Origin, Evolution, and Modern Aspects of Biomineralization in Plants and Animals, 103-124. https://doi.org/10.1007/978-1-4757-6114-6_8

    Harley, C. D. (2008). Tidal dynamics, topographic orientation, and temperature-mediated mass mortalities on rocky shores. Marine Ecology Progress Series, 371, 37-46. https://doi.org/10.3354/meps07711

    Høeg, J. T., & Møller, O. S. (2006). When similar beginnings lead to different ends: Constraints and diversity in cirripede larval development. Invertebrate Reproduction & Development, 49(3), 125-142. https://doi.org/10.1080/07924259.2006.9652204

    Kamino, K. (2016). Barnacle underwater attachment. Biological Adhesives, 153-176. https://doi.org/10.1007/978-3-319-46082-6_7

    Qian, P., Lau, S. C., Dahms, H., Dobretsov, S., & Harder, T. (2007). Marine Biofilms as mediators of colonization by marine Macroorganisms: Implications for antifouling and aquaculture. Marine Biotechnology, 9(4), 399-410. https://doi.org/10.1007/s10126-007-9001-9

    Southward, A. J. (2008). Barnacles: Keys and notes for the identification of British species. Field Studies Council. Yu, S., & Chan, B. K. (2020). Intergenerational microplastics impact the intertidal barnacle Amphibalanus Amphitrite during the planktonic larval and benthic adult stages. Environmental Pollution, 267, 115560. https://doi.org/10.1016/j.envpol.2020.115560