Sharks of Onslow County

Category: Biogeochemical Cycles

Slough Mud: The Gooey, Stinking Ecosystem Beneath Onslow County’s Shoreline

Where the Ground Doesn’t Hold

There are places along the edges of the water in Onslow County where the ground stops behaving like ground.

You find them along the sound side, at the margins of tidal creeks, and in the quieter edges of channels that drain toward New River Inlet. Places like the shallows near Soundside Park or the creek edges around Kenneth D. Batts Family Park look ordinary when the tide is in—flat water, sometimes with a darker tone beneath the surface, but otherwise unremarkable.

As the tide pulls away, that surface is left behind, exposed in a way that suggests continuity, as though it will hold underfoot the same way sand does along the open beach.

It holds just long enough to believe that.

Then it gives way.

A step sinks past the ankle before there is time to adjust, and the next carries deeper, the sediment tightening around your leg—not suddenly, but with a steady resistance that makes each movement slower than expected, until pulling free requires more effort than the surface first suggested and the footing you thought you had no longer offers anything solid to push against.

Sometimes the mud keeps what you brought with you.

It holds—until it doesn’t. | Image credit: Florida Tech

Each step releases a faint, unmistakable sulfur smell from below, brief but distinct, rising as the sediment shifts and settling again as it closes around the space you’ve displaced.

Nothing about it suggests stability, and yet nothing about it is still.

Where It Forms: Water That Slows Down

If you step back—onto firmer ground, where your footing holds—the pattern begins to show itself.

These places gather along edges where water loses momentum. Along the sound side, there are no breaking waves to constantly overturn the bottom. Water moves in, spreads thin across the flats, and then drains back through the same narrow paths, slowing as it goes.

When that movement slows, what the water was carrying no longer stays suspended.

Fine silts and clays begin to settle. Fragments of marsh grass drift down. Microscopic shells and organic particles—too small to notice while they are moving—collect layer by layer until the bottom changes character (Folk, 1980; Riggs et al., 2008).

Much of that material begins only a few feet away.

Where the water slows, what it carries begins to settle. | Image credit: A. Mitchell

Along the edges of these creeks, smooth cordgrass—Spartina alterniflora—holds the shoreline in place. When it dies back, it doesn’t disappear. It breaks apart, and with each tide, that material moves outward. What looks like loss becomes movement—organic matter carried away from the marsh and into these quieter edges (Odum, 1980).

Where the water lingers, that material accumulates.

And over time, accumulation becomes something you can step into.

The Surface: What Almost Holds

From above, it can look continuous.

In certain light—especially when the sun is low—there is a faint sheen across the surface, something smoother and more uniform than water alone would create. It can appear firm enough to cross, at least for a step or two.

That thin layer is not just sediment.

It settles just enough to look stable—until the weight shifts. | Image credit: A. Mitchell

Microscopic organisms—diatoms and cyanobacteria—spread across the surface, forming a film that binds particles together. They produce substances that hold grains in place, creating a surface that can briefly support weight before it gives way beneath it (Rimmer et al., 2025).

It is just enough structure to mislead you.

Just enough to suggest that what lies beneath it will behave the same way.

Why It Gives Way: Structure Without Support

Once that surface breaks, the difference becomes immediate.

The particles here are small enough to trap water between them, and once that water is there, it does not drain the way it does through sand. The sediment remains saturated, and when pressure is applied, the water has nowhere to go.

Instead of holding its shape, the ground shifts.

There is a way to describe how well a surface resists that kind of movement—shear strength. Sand has enough of it to support your weight.

This does not (Folk, 1980).

There’s form here, but no support—only water and loosened sediment. | Image credit: A. Mitchell

And beneath the surface, the structure is already interrupted. Burrows open and collapse. Small voids form and disappear. Gas collects in pockets that shift when disturbed. What looks continuous from above is already moving below.

So when your foot sinks, it is not breaking through something solid.

It is entering something that was never still to begin with.

Below the Surface: Where the Air Runs Out

The smell arrives as soon as the surface opens.

It rises quickly, sharp and distinct, and then fades again as the mud closes.

Just beneath the surface, oxygen is used up rapidly by microorganisms breaking down the organic material that has accumulated there. Below that thin layer, the sediment becomes anoxic—oxygen is no longer present (Fenchel & Riedl, 1970; Jørgensen & Nelson, 2004).

But the process doesn’t stop.

Bacteria continue to break material down, using sulfate from seawater instead of oxygen. That shift produces hydrogen sulfide gas, which remains trapped until the sediment is disturbed (Kasten & Jørgensen, 2000).

Each step releases it.

The smell is not separate from the system. It is evidence that the breakdown is still happening—just without air.

And because it is happening without oxygen, it happens more slowly.

What Stays Behind

If that same plant material were left exposed to air, it would break down quickly. Most of what it contains would return to the atmosphere as carbon dioxide.

Here, much of it does not.

The organic material that settles into this mud—marsh grass, algae, microscopic debris—is buried into a system where oxygen disappears almost immediately. Without that oxygen, decomposition slows, and a portion of that carbon remains stored in the sediment instead of returning to the air (Chmura et al., 2003).

It does not stop changing.

It is broken down, reworked, and shifted. But it is not fully released.

Layer after layer builds beneath the surface—material that was once living, now held within the mud you step into.

What smells like decay is also storage.

The Surface Is Breathing

Even without oxygen below, the surface is not sealed.

If you stand still long enough, you begin to see small openings, slight movements, places where the mud seems to shift or pulse.

Water moves in and out with the tide. Burrows connect the surface to what lies below. Worms, shrimp, and crabs pull oxygenated water downward as they move through the sediment (Aller, 1982; McCave, 1976).

And the plants at the edge are part of it too.

Marsh grasses do not just sit in the mud. They move oxygen from the air above down into their roots. Some of that oxygen leaks into the surrounding sediment, creating small zones where oxygen briefly exists before it is used up again.

It is uneven. Temporary. Constantly shifting.

At the surface, gases move both ways.

Oxygen enters. Carbon dioxide leaves. Small amounts of other gases—products of what is happening below—escape when the sediment is disturbed or when pressure changes with the tide.

The boundary is thin.

But it is active.

Movement You Don’t See

If you stop looking for stable ground and begin watching the surface itself, other patterns start to emerge.

What looks still is already in use. | Image credit: A. Mitchell

Small openings appear—round, spaced in ways that suggest something below rather than something left behind. Around them, slight mounds form and disappear as the mud dries and softens again.

These are not marks left on the surface. They are the surface expression of what is moving through it.

Polychaete worms pass through the sediment, ingesting it and depositing what remains behind them (Rhoads, 1974). Burrowing shrimp and amphipods maintain tunnels that allow water—and with it, oxygen—to move deeper into the mud than it otherwise could (Aller, 1982).

Crabs hold the edges.

Fiddler crabs open and close their burrows with the tide. Blue crabs move through when water returns, feeding within the same soft substrate that gives way underfoot. Mud crabs remain within it, emerging only when conditions allow.

Bivalves stay buried beneath it all, filtering water when submerged, holding position when exposed.

Sometimes you don’t see them until you feel them.

A sharp edge beneath your foot where the mud shifted just moments before.

The surface does not tell you everything that is there.

When the Water Returns

Then the water comes back.

It fills the same space that resisted your footing, covering the surface without changing what lies beneath it. The ground that gave way becomes part of a shallow, moving system again.

Fish arrive with the water.

Killifish move into these margins first, tolerating the low oxygen conditions that remain in the sediment. Flounder settle directly onto the bottom, their bodies flattening, their coloration shifting until they disappear against it.

Juvenile blue crabs move through these same areas, using them as nursery habitat—protected, shallow, and full of food (Bilkovic et al., 2020).

They are not just using the space. They are feeding on what the mud is processing.

Detritus, microbes, and organic material move through the system below the surface, supporting what arrives above it.

Other species follow.

Stingrays glide over the surface, feeding on what is buried below. Croaker move through slightly deeper channels. Along exposed flats near The Point at Topsail Beach, shorebirds track the retreating tide—probing, picking, following the movement of water as it exposes and covers the same ground again.

As the water returns, the surface changes—and life moves with it. | Image credit: A. Mitchell

What looked still becomes active.

Not because it changed.

But because the conditions around it did.

What Comes From the Marsh

At the edge where your footing gave way, the connection is already there.

The marsh does not end where the grass stops. It extends outward through what it releases.

This isn’t separate from the marsh—it’s what the marsh leaves behind. | Image credit: A. Mitchell

The grasses along the shoreline slow the water, trapping sediment and holding the edge in place. During storms, they absorb energy that would otherwise move inland, reducing erosion and limiting how much material is carried away (Barbier, 2012).

But they also export material.

As grasses break down, they move with the tide—out of the marsh, into the creeks, and into these quieter margins where the water slows again.

What settles here is not separate from the marsh.

It is what the marsh becomes once it begins to move—and what it leaves behind when it does.

What Changes, and What Doesn’t

The ground beneath you is not fixed.

Periods of calm allow fine sediments to build, thickening the layer and increasing the amount of organic material held within it. Warmer temperatures increase microbial activity, accelerating what is happening below the surface.

A storm can undo that quickly.

Sediment lifts back into the water, moves elsewhere, and settles in new places. Edges shift. Channels deepen or fill. What held you in place one week may not exist in the same way the next (Pilkey et al., 2014).

Other changes move more slowly.

Development alters how water flows. Marsh edges are reduced or hardened. Invasive plants like Vitex rotundifolia change how sediment is captured and released.

The system continues.

But the way it moves through the landscape can change.

Standing at the Edge of It

Standing at the edge of one of these places, it is easy to focus on the moment your footing failed—the way the ground gave way when it seemed like it shouldn’t.

But nothing about it failed.

What felt unstable is a working layer—one that gathers what the marsh releases, slows its return to the air, supports what can move within it, and disappears beneath the water as the tide returns.

The same ground that held you in place becomes part of something continuous again, connected to marsh, creek, sound, and ocean.

It does not hold because it is not meant to.

It holds because it is already in motion.

Nothing here failed—it’s doing exactly what it’s meant to do. | Image credit: A. Mitchell

References

Able, K., Manderson, J., & Studholme, A. (1999). Habitat quality for shallow water fishes in an urban estuary:the effects of man-made structures on growth. Marine Ecology Progress Series, 187, 227-235. https://doi.org/10.3354/meps187227

Aller, R. C. (1982). The effects of Macrobenthos on chemical properties of marine sediment and overlying water. Topics in Geobiology, 53-102. https://doi.org/10.1007/978-1-4757-1317-6_2

Barbier, E. B. (2012). Progress and challenges in valuing coastal and marine ecosystem services. Review of Environmental Economics and Policy, 6(1), 1-19. https://doi.org/10.1093/reep/rer017

Bilkovic, D., Isdell, R., Stanhope, D., Angstadt, K., Havens, K., & Chambers, R. (2021). Nursery habitat use by juvenile blue crabs in created and natural marshes. Ecological Engineering, 170(106333). https://doi.org/10.1016/j.ecoleng.2021.106333

Chmura, G. L., Anisfeld, S. C., Cahoon, D. R., & Lynch, J. C. (2003). Global carbon sequestration in tidal, saline wetland soils. Global Biogeochemical Cycles, 17(4). https://doi.org/10.1029/2002gb001917

Fenchel, T. M., & Riedl, R. J. (1970). The sulfide system: A new biotic community underneath the oxidized layer of marine sand bottoms. Marine Biology, 7(3), 255-268. https://doi.org/10.1007/bf00367496

Folk, R. L. (1980). Petrology of sedimentary rocks (2nd ed.). Hemphill Publishing Company.

Jørgensen, B. B., & Nelson, D. C. (2004). Sulfide oxidation in marine sediments: Geochemistry meets microbiology. Sulfur Biogeochemistry – Past and Present. https://doi.org/10.1130/0-8137-2379-5.63

Kasten, S., & Jørgensen, B. B. (2000). Sulfate Reduction in Marine Sediments. In Marine Geochemistry (pp. 263-264). Springer, Berlin, Heidelberg.
https://doi.org/10.1007/978-3-662-04242-7_8

McCave, I. N. (1976). Organism-Sediment Relationships. In The Benthic Boundary Layer (pp. 273-295). Plenum Press.

Odum, E. P. (1980). The status of three ecosystem-level hypotheses regarding salt marsh estuaries: Tidal subsidy, outwelling, and detritus-based food chains. Estuarine Perspectives, 485-495. https://doi.org/10.1016/b978-0-12-404060-1.50045-9

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.

Riggs, S. R., Ames, D. V., & Dawkins, K. R. (2008). Coastal processes and conflicts: North Carolina’s Outer Banks: A curriculum for middle and high school students (NCU-E-08-002). NOAA Oceanic and Atmospheric Research; Sea Grant. https://repository.library.noaa.gov/view/noaa/46454/noaa_46454_DS1.pdf

Rimmer, J., Blight, A., Chocholek, M., & Paterson, D. (2025). Response of natural estuarine Microphytobenthic Biofilms to multiple anthropogenic stressors. Environmental Pollution, 387(127285). https://doi.org/10.1016/j.envpol.2025.127285

April 25, 2026
When the Bottom Moves: Rays in the Shallows of Onslow County

What People Are Seeing

In the last few weeks, the water along the edges of Onslow County has felt different.

Not because the water itself has changed—but because something beneath it has become harder to ignore.

Schools of cownose ray (Rhinoptera bonasus) move just below the surface nearshore, their wingbeats lifting faint clouds from the bottom as they pass. In the soundside shallows, where the water thins over sand and mud, Atlantic stingray (Hypanus sabinus) settle into the substrate, half-buried and nearly invisible until a step comes too close and the outline breaks.

People are seeing them more often now—but they’re also reacting to them.

A pause mid-step in shallow water.
A quick shift backward when something moves.
Fishermen lifting a line and stopping for a second longer than usual—not what they expected to find.

There is awe in it.

And sometimes hesitation.

Because the same thing that makes them easy to notice now also makes them easy to miss.

The question follows quickly:

Are there more of them this year?

Maybe.

But that question lingers longer than the answer.

Cownose rays migrating in Swansboro, NC. | Image credit: Pogie’s Academy

What Brings Them Here

As spring settles in along the North Carolina coast, the system begins to reorganize.

Water temperatures rise, and with that rise comes a shift in metabolism. Rays—like many coastal species—become more active as conditions move into a narrower range that supports feeding and movement (Smith & Merriner, 1987; Schwartz & Dahlberg, 1978).

For cownose rays, this seasonal transition includes a northward migration along the Atlantic coast, bringing large groups into nearshore and estuarine waters (Smith & Merriner, 1987).

Large groups of cownose rays like these move north along our coast each season, arriving together in shallow water. | Image credit: Vidyacharan A. Alchi

But movement alone does not explain what people are seeing.

What matters is where that movement meets the structure of the environment.

The water does not always look the same—some days it is flat and clear enough to see straight to the bottom, and other days the slightest movement turns it cloudy, changing what can be seen and what remains hidden (Peterson et al., 2001).

And beneath all of it is food.

Cownose rays move through the shallows, sweeping across the bottom and disrupting what lies beneath them, crushing clams, oysters, and other shelled invertebrates with broad, flattened tooth plates (Collins et al., 2007; Fisher, 2010).

Atlantic stingrays hold low against the bottom, burying into the sand as they feed and working within the sediment itself—not moving across it—uncovering and drawing in small invertebrates hidden below (Snelson et al., 1988; Schwartz & Dahlberg, 1978).

Atlantic stingrays hold close to the bottom, often blending in until something shifts and gives them away. | Image credit: Andy Murch

Where prey is accessible, rays follow.

Where prey is concentrated in shallow, warming water, rays do not just pass through—they stay, turn, feed, and linger.

And in doing so, they cross into the same narrow band of space where people enter the water (Bangley et al., 2018).

They are not simply “here more.”

They are here in ways—and in places—that make them visible.

What Happens When They Feed

When a ray feeds, the bottom does not remain the same.

A cownose ray moving across a flat is not just searching—it is actively restructuring the surface beneath it. As it passes, the bottom is turned over behind it, patches of sand and mud disturbed where clams and other buried life have just been uncovered and crushed (Peterson et al., 2001; Smith & Merriner, 1985).

Feeding pits left behind by rays. Easy to mistake for crab holes at first—until you start to recognize the pattern and what’s actually shaping the bottom. | Image credit: Giaroli et al., 2024

Atlantic stingrays leave a different kind of trace. Where they settle, the surface shifts more subtly—small depressions, softened patches, places where the sediment has been worked rather than overturned, as buried invertebrates are uncovered and drawn in (Snelson et al., 1988; Schwartz & Dahlberg, 1978).

This is bioturbation—the bottom being reworked by the animals moving through it and within it (Thrush & Dayton, 2002).

As they feed, the bottom lifts into the water—fine particles rising and hanging there, turning clear water slightly cloudy (Thrush & Dayton, 2002).

The water does not stay still—the bottom here is constantly shifting, the way much of this coastline does, even when it appears unchanged.

And neither does the system.

Oysters and clams quietly filter the water as they feed, and when their numbers shift—even in small areas—the water and everything moving through it begins to change with them (Newell, 2004; zu Ermgassen et al., 2013).

In places where rays have been feeding, those filtering communities can be reduced or redistributed (Peterson et al., 2001).

Not removed entirely—but changed.

And that change does not stay in one place.

It moves outward, carried in the way the water looks, the way it settles, and what it can hold.

Layers of the Food Web

Rays do not sit at the top of the system, and they are not at the bottom of it.

As mesopredators, they feed on what is buried in the sediment, but they are also available to what moves through the water above. That position—between—links parts of the system that do not often meet directly (Myers et al., 2007; Heithaus et al., 2008).

What they do in that space matters.

As cownose rays move through andAtlantic stingrays work within the bottom, they are not just feeding—they are shaping what persists there. Clams, oysters, and other invertebrates do not simply accumulate unchecked. Their numbers are reduced, redistributed, and in some places kept from becoming dominant (Peterson et al., 2001).

Movement like this doesn’t stay in one place for long.

That pressure shapes the bottom itself.

Bivalves filter the water. Invertebrates stabilize sediment. When their abundance shifts, the system responds—sometimes toward clearer water, sometimes toward more suspended material, depending on what remains and where (Newell, 2004; zu Ermgassen et al., 2013).

Rays do not create those conditions alone—but they influence which direction the system moves.

At the same time, they carry that energy upward.

Juvenile sharks moving through these shallow waters encounter not just prey, but a system already in motion—areas where the bottom has been disturbed, where feeding has recently occurred, where something has been uncovered or displaced (Bangley et al., 2018).

And in some cases, the rays themselves become part of that exchange.

This is what it means to sit in the middle.

Not just connecting layers—but regulating how energy and movement pass between them.

If that middle shifts, the balance does not disappear.

It changes direction.

Why It Feels Sudden

There is a moment, standing in shallow water, when the bottom stops feeling like something you can trust.

What looked like sand shifts.
What felt still is no longer still.

Sometimes you notice it in time—a shape lifting away, a shadow moving just beneath the surface. A plume of fine sediment rising to the surface under a paddleboard with a trail following it.

The moment when the bottom stops looking empty. | Image credit: iStock

Sometimes you don’t.

A step comes down where something is already settled.
Hidden in the sand.
Working within it.

The reaction is immediate.
Surprise first. Then pain. Then the realization of what was there all along.

It is easy, in that moment, to think something unexpected has happened—the same kind of sudden awareness that comes when something just beneath the surface reveals itself.

But what you are stepping into is not a single event.

It is a convergence.

Water temperatures have risen, bringing rays into the shallows as they feed and move through these systems (Smith & Merriner, 1987; Schwartz & Dahlberg, 1978).

Tides narrow the space, concentrating movement into a thinner band of water.

The bottom has already been worked—turned by cownose rays moving through, disturbed by Atlantic stingrays holding within it.

And at the same time, people have returned to the water.

For a brief window, all of it overlaps.

Not more.
But more visible.

It feels sudden because you are standing at the point where all of these things meet.

And for a moment, the system lets you see it.

References

Bangley, C. W., Paramore, L., Dedman, S., & Rulifson, R. A. (2018). Delineation and mapping of coastal shark habitat within a shallow lagoonal Estuary. PLOS ONE, 13(4), e0195221. https://doi.org/10.1371/journal.pone.0195221

Giaroli, M. L., Byrne, I., Gilby, B. L., Taylor, M., Chargulaf, C. A., & Tibbetts, I. R. (2024). The distribution and significance of stingray feeding pits in Quandamooka (Moreton Bay), Australia. Marine and Freshwater Research, 75(18). https://doi.org/10.1071/mf23247

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

Kolmann, M. A., Huber, D. R., Motta, P. J., & Grubbs, R. D. (2015). Feeding biomechanics of the cownose ray, Rhinoptera bonasus, over ontogeny. Journal of Anatomy, 227(3), 341-351. https://onlinelibrary.wiley.com/doi/full/10.1111/joa.12342

Myers, R. A., Baum, J. K., Shepherd, T. D., Powers, S. P., & Peterson, C. H. (2007). Cascading effects of the loss of APEX predatory sharks from a coastal ocean. Science, 315(5820), 1846-1850. https://doi.org/10.1126/science.1138657

Newell, R. I. (2004). Ecosystem influences of natural and cultivated populations of suspension-feeding bivalve molluscs: A review. 23(1), 51–61. Journal of Shellfish Research, 23(1), 51-61. https://go.gale.com/ps/i.do?id=GALE%7CA118543914

Peterson, C. H., Fodrie, J. F., Summerson, H. C., & Powers, S. P. (2001). Site-specific and density-dependent extinction of prey by schooling rays: generation of a population sink in top-quality habitat for bay scallops. Oecologia, 129, 349-356. https://link.springer.com/article/10.1007/s004420100742

Schwartz, F. J., & Dahlberg, M. D. (1978). Biology and ecology of the Atlantic Stingray, Dasyatis Sabina (Pisces: Dasyatidae) in North Carolina and Georgia. Northeast Gulf Science, 2(1). https://doi.org/10.18785/negs.0201.01

Smith, J. W., & Merriner, J. V. (1985). Food habits and feeding behavior of the Cownose ray, Rhinoptera bonasus, in lower Chesapeake Bay. Estuaries, 8(3), 305. https://doi.org/10.2307/1351491

Smith, J. W., & Merriner, J. V. (1987). Age and growth, movements and distribution of the Cownose ray, Rhinoptera bonasus, in Chesapeake Bay. Estuaries, 10(2), 153. https://doi.org/10.2307/1352180

Snelson, F. F., Williams-Hooper, S. E., & Schmid, T. H. (1988). Reproduction and ecology of the Atlantic Stingray, Dasyatis Sabina, in Florida coastal lagoons. Copeia, 1988(3), 729. https://doi.org/10.2307/1445395

Thrush, S. F., & Dayton, P. K. (2002). Disturbance to marine benthic habitats by trawling and dredging: Implications for marine biodiversity. Annual Review of Ecology and Systematics, 33(1), 449-473. https://doi.org/10.1146/annurev.ecolsys.33.010802.150515

Zu Ermgassen, P. S., Spalding, M. D., Blake, B., Coen, L. D., Dumbauld, B., Geiger, S., Grabowski, J. H., Grizzle, R., Luckenbach, M., McGraw, K., Rodney, W., Ruesink, J. L., Powers, S. P., & Brumbaugh, R. (2012). Historical ecology with real numbers: Past and present extent and biomass of an imperilled estuarine habitat. Proceedings of the Royal Society B: Biological Sciences, 279(1742), 3393-3400. https://doi.org/10.1098/rspb.2012.0313

April 11, 2026
Winter at the Exposed Marsh

The surface that appears

At low tide in winter the creek mouths behind Topsail Island widen into ground that is usually concealed, and the exposed marsh does not appear emptied so much as translated into another state where water has thinned into channels narrow enough to reveal the structure it normally masks. The flats emerge as a textured plane stitched by the remains of Spartina alterniflora, each stem cluster surrounded by a faint collar of darker mud where drainage lags by seconds, and the surface separates into alternating bands that hold or soften depending on how recently porewater escaped. This firmness reflects sediment consolidation, the gradual compression of mud as water drains between tides, tightening elevated shelves first and leaving adjacent troughs saturated, so the exposed ground becomes a map of load-bearing ridges that anticipates where larger animals will move once the marsh opens (Christiansen et al., 2000; Morris et al., 2002).

Close to the surface, winter resolves into finer evidence that the marsh is neither dormant nor still. Fiddler crab chimneys crumble into damp grains that expose darker sediment beneath a thin crust, while hoofprints from the previous tide hold shallow mirrors rimmed with frost where a faint olive sheen gathers as diatoms trap warmth and moisture (Underwood & Kromkamp, 1999). Beside the prints, spirals of fine sediment rise like coiled handwriting, polychaete casts lifted from below and dried into granular ridges that record upward movement from buried layers. Every centimeter of mud registers exchange between subsurface metabolism and cold air, and the exposed flats behave less like the absence of water than a temporary reorganization of it, one that prepares a surface already structured for the next set of crossings.

Clusters of crab burrow openings mark the marsh surface, each hole a vertical conduit linking oxygen, water, and nutrients to the sediment below. | Photo credit: M. Mitchell, 2026

Where winter concentrates energy

The winter low tide exposes more than terrain, because the withdrawal of water aligns accessibility with abundance in a way that concentrates food at the surface for a brief interval. Spartina rhizomes lie just beneath the crust, their pale ends visible where deer have bitten through the mud, and detached stems gather in wrack lines where microbial films soften fibrous blades into digestible pulp. Small bivalves remain gaping in shallow pools where temperature lingers above the surrounding flats, and worm casts cluster where organic matter has settled densely enough to support continuous feeding below. This alignment functions as a resource pulse, a moment when energy stored in buried plant tissue and invertebrate biomass becomes reachable simultaneously.

Wrack concentrated by winter tides stores organic energy in dense bands, drawing shorebirds to feed where nutrients accumulate along the marsh edge. | Photo credit: American Birding Association

Deer enter the marsh along consolidated ridges that hold their weight, yet the crossings do not run straight through these zones of exposure but instead loop and return around feeding sites where sediment has been churned darker than its surroundings. The mud at these points holds fragments of torn rhizomes pressed into its surface and shredded plant fibers mixed into the crust, while overlapping tracks form shallow basins that later fill with water and preserve the geometry of the feeding circuit. Raccoon prints braid across the same lines, Canada goose droppings mark cropped stems, and dunlin and greater yellowlegs settle repeatedly where the surface softens under pressure, their bills puncturing the crust in arcs that echo the paths carved by hooves. Exposure redistributes energy upward, and movement gathers along the same ridges that consolidation established, tying feeding to structure without separating the two processes.

The skin that reforms

Cross-section of marsh sediment showing deposition, erosion, and consolidation, the shifting layers that form and reform the exposed winter surface. | Graphic credit: G. S. Sylvain, 2011

Between exposures, slack water leaves a thin veneer that dries into a continuous surface film through sediment sealing, a layer fine enough to slow the exchange of gases between air and mud (Christiansen et al., 2000). When intact, the flats dull into a flexible sheet that bends faintly under weight, and breaking it releases a muted sulfur odor that signals redox cycling, the shift between oxygenated and oxygen-poor states driven by microbial respiration in buried sediment (Howarth & Teal, 1979; Mendelssohn et al., 1981). Color reveals the chemistry more reliably than smell. Black veins branch through exposed mud where iron binds sulfide, while pale halos surround Spartina roots where oxygen leaks downward along living tissues.

Each footprint becomes an aperture in this membrane, allowing oxygen to enter and reduced compounds to rise, so the breach brightens temporarily before darkening again as metabolism rebalances. Feeding animals convert chemical gradients into visible patterns, and the flats accumulate a shifting mosaic of sealed and reopened zones that migrate with every tide, ensuring that the next exposure inherits the chemical memory of the previous one.

$Tracks fracture the sealed winter crust, revealing darker sediment where oxygen re-enters and the surface begins to reform. | Photo Credit: M. Gold, 2023$
Tracks fracture the sealed winter crust, revealing darker sediment where oxygen re-enters and the surface begins to reform. | Photo Credit: M. Gold, 2023

The ground below the ground

Beneath the crust, the sediment continues to reorganize through bioturbation, the mixing of mud by infaunal animals whose activity does not cease with falling temperature. Polychaete worms thread galleries through the upper layers, lifting sediment to the surface in tight spirals while their burrows act as ventilation shafts through burrow ventilation, drawing oxygen downward and leaking reduced porewater upward (Kristensen, 2000; Aller, 1982). Small bivalves pump water through siphons that leave paired pinholes scattered across the flats, and amphipods graze biofilms coating the worm casts, linking subsurface feeding to surface texture.

Each round of burrowing lifts buried debris and nutrients toward the surface, making crab tunnels pathways that continually rebuild the marsh from below. | Graphic credit: Wang et al., 2010

Where deer cross and feed, hooves collapse some tunnels while sealing others, producing prints that darken unevenly because subsurface architecture differs from step to step. The feeding circuits therefore overlay hidden engineering that maintains permeability and redistributes nutrients, ensuring that exposure, grazing, and burrowing operate as one continuous process rather than as isolated events separated by layers of mud.

Smell in shallow water

Disturbed sediment releases dissolved compounds that spread through shallow pools as porewater plumes, chemical gradients that extend beyond the visible cloud of suspended mud. Killifish and juvenile mullet navigate these gradients through chemoreception, keeping their snouts close to the surface while pivoting toward intensifying scent (Kneib, 1997; Kristensen, 2000). Their feeding loosens additional sediment and amplifies the plume before particles settle again, creating a moving field of chemical information that overlaps with the physical contours of the flats.

What appears from above as a brief swirl becomes a signal that attracts birds, and dunlin and yellowlegs converge on fresh pits where worms remain exposed. Each crater fills with water and darkens as sulfide seeps upward, and feeding layers stack in sequence so that invertebrate disturbance leads to fish excavation, which leads to avian probing, all anchored to the same exposure that first drew deer into the marsh. Leaning close reveals faint popping as methane and carbon dioxide escape through gas ebullition, ticking upward from saturated sediment while animals feed across the surface. The marsh ventilates audibly, and the sound marks exchange continuing beneath apparent stillness.

As the tide withdraws, exposed mud concentrates scent and invertebrates near the surface, guiding shorebirds to feeding zones written into the sediment. | Photo credit: Ron Watts

Memory in the surface

Winter tides and storms deposit sediment that raises the marsh through vertical accretion, stacking particles in increments small enough to disappear into the surface unless read over time (Morris et al., 2002). Hurricane overwash leaves thin sand sheets that redirect drainage for months, oyster clusters trap suspended grains in their lee (Newell et al., 2005), and worm burrows stabilize some deposits while loosening others (Kirwan & Megonigal, 2013). Feeding compresses ridges and excavation softens troughs, embedding each disturbance into the next layer so that the flats carry a structural memory of their own use.

Returning after weeks reveals crossings shifted, wrack lines buried, and worm casts clustered in new zones, evidence that the marsh does not reset between exposures but accumulates the imprint of repeated winter engineering.

Winters that change

Warmer temperatures extend microbial activity through temperature-driven metabolic acceleration, thinning the interval between sealing and decay and allowing chemical gradients to persist longer at the surface (Bridgham et al., 2006). Rising water levels narrow exposure windows, stronger storms redistribute sediment in thicker pulses, and shifting coastal currents alter nutrient delivery and larval supply, influencing which species occupy the winter flats (Kirwan & Megonigal, 2013). The marsh continues to open, yet the rhythm of exposure recalibrates, and feeding circuits migrate toward higher shelves where consolidation still holds.

Chemical plumes stretch farther in warmer water, grazing concentrates into narrower bands, and the same negotiations between structure and feeding repeat under altered timing, ensuring that winter engineering continues without preserving its previous schedule.

Seasonal temperature outlook showing shifting winter probabilities across the southeastern United States, a regional signal that filters down to marsh-level processes. | NOAA – National Weather Service, 2026

The surface in motion

The creek mouth appears quiet until attention lowers to the scale of sediment. Frost melts along print rims before surrounding crust warms, gas ticks upward through worm tubes, fish pits refill, and diatoms bloom where warmth collects. Each tide writes another layer into a system held in dynamic equilibrium, continuous adjustment that maintains form while never remaining fixed (Morris et al., 2002). Exposure leads to feeding, feeding reshapes structure, and structure governs the next exposure as the marsh opens again.

The same ridges that hold a deer’s weight will soften again when the tide returns, and the feeding circuits traced across them will dissolve into channels that redistribute the next layer of sediment. Worm burrows will reopen where hooves sealed them, chemical plumes will reassemble in newly flooded pools, and the surface will carry forward the imprint of this exposure into the next one. Winter does not suspend the marsh. It recalculates it at a slower tempo, redistributing energy across the same structures that will support spring growth and summer density, so that even in the coldest intervals the creek mouth continues its quiet accounting of exchange, preparing another surface that will open and be read again.

Deer cross the marsh to reach winter feeding exposed by the tide, moving along corridors that appear only when the surface opens. | Photo credit: L. W. Hamilton, 2025

References

Aller, R. C. (1982). The effects of Macrobenthos on chemical properties of marine sediment and overlying water. Topics in Geobiology, 53-102. https://doi.org/10.1007/978-1-4757-1317-6_2

Bridgham, S. D., Megonigal, J. P., Keller, J. K., Bliss, N. B., & Trettin, C. (2006). The carbon balance of North American wetlands. Wetlands, 26(4), 889-916. https://doi.org/10.1672/0277-5212(2006)26[889:tcbona]2.0.co;2

Christiansen, T., Wiberg, P., & Milligan, T. (2000). Flow and sediment transport on a tidal salt marsh surface. Estuarine, Coastal and Shelf Science, 50(3), 315-331. https://doi.org/10.1006/ecss.2000.0548

Howarth, R. W., & Teal, J. M. (1979). Sulfate reduction in a New England salt marsh1. Limnology and Oceanography, 24(6), 999-1013. https://doi.org/10.4319/lo.1979.24.6.0999

Kirwan, M. L., & Megonigal, J. P. (2013). Tidal wetland stability in the face of human impacts and sea-level rise. Nature, 504(7478), 53-60. https://doi.org/10.1038/nature12856

Kneib, R. T. (1997). The role of tidal marshes in the ecology of estuarine nekton. Oceanography And Marine Biology, 35(35), 159-216. https://doi.org/10.1201/b12590-5

Kristensen, E. (2000). Organic matter diagenesis at the oxic/anoxic interface in coastal marine sediments, with emphasis on the role of burrowing animals. Hydrobiologia, 426(1), 1-24. https://doi.org/10.1023/a:1003980226194

Mendelssohn, I. A., McKee, K. L., & Patrick, W. H. (1981). Oxygen deficiency in Spartina alterniflora roots: Metabolic adaptation to anoxia. Science, 214(4519), 439-441. https://doi.org/10.1126/science.214.4519.439

Morris, J. T., Sundareshwar, P. V., Nietch, C. T., Kjerfve, B., & Cahoon, D. R. (2002). Responses of coastal wetlands to rising sea level. Ecology, 83(10), 2869. https://doi.org/10.2307/3072022

Newell, R. I., Fisher, T. R., Holyoke, R. R., & Cornwell, J. C. (2005). Influence of eastern oysters on nitrogen and phosphorus regeneration in Chesapeake Bay, USA. NATO Science Series IV: Earth and Environmental Series, 282, 93-120. https://doi.org/10.1007/1-4020-3030-4_6

Underwood, G., & Kromkamp, J. (1999). Primary production by phytoplankton and Microphytobenthos in estuaries. Advances in Ecological Research, 29, 93-153. https://doi.org/10.1016/s0065-2504(08)60192-0

February 7, 2026
The Leftovers: What Happens to Summer’s Prey When the Big Fish Leave?

The Quiet Season Begins

When the red drum, flounder, and summer sharks follow the cooling tides offshore, Onslow County’s estuaries fall quiet. The flashy chases fade, and the splashes that once rippled through the creeks give way to stillness. But the story doesn’t end. Beneath November’s calm water, the estuary begins to rewrite itself.

The absence of its top hunters leaves behind both energy and opportunity — a banquet for the small and the overlooked. The currents no longer echo with the heavy pulse of pursuit. Instead, what remains is a more deliberate rhythm — a slow exchange between detritus, crabs, and the smaller fish that endure the cold months ahead.

Winter in the New River Estuary: The Vacancy in the Food Web

Every migration leaves an ecological vacancy. When red drum and southern flounder depart, they take with them both predatory pressure and nutrient export. The estuary briefly relaxes its guard. Prey fish, shrimp, and crabs experience a momentary release from predation from top predator populations that cause a cascade that momentarily alters predation pressure on lower-level prey (Clark et al., 2003).

In this lull, energy that once fueled apex biomass lingers in the system, stored in crustaceans and schooling fish that escaped the hunt (Baird et al., 1998). The estuary, ever adaptive, redistributes that energy downward. Blue crabs (Callinectes sapidus) and juvenile spot (Leiostomus xanthurus) surge in number, exploiting the leftovers of summer’s feast (Allen et al., 2024). The marsh becomes a recycling ground — energy looping through smaller players instead of flowing outward to the sea.

Late-fall estuarine food web diagram showing energy flow from detritus to shrimp, fish, and mesopredators.

The Winter Guardians

But not all predators have gone. When the warm-water hunters leave, colder visitors arrive. Along the inlets and nearshore waters of Onslow Bay, Atlantic spiny dogfish (Squalus acanthias) drift in with the falling temperatures. They are the quiet inheritors of the season — small sharks with silver eyes and slate-gray backs, moving in disciplined schools just offshore.

Atlantic spiny dogfish (Squalus acanthius) — the “winter guardians” — patrol coastal waters when larger predators have departed, sustaining the rhythm of predation. | Photo credit: Andy Murch

Where the big sharks of summer — sandbars, blacktips, and bulls — have vanished southward or deeper, the dogfish remain. Their bodies are built for cold water, thriving where others slow (Carlson et al., 2014). And while their size may not inspire awe, their purpose is no less vital: they fill the empty seats at the top of the table.

Dogfish are mesopredators, but in winter they act as temporary apex hunters, patrolling the inlet and inner shelf where menhaden, herring, and squid still linger (Carlson et al., 2014). Their presence keeps the ecosystem in motion. They thin out the schools that might otherwise explode in number, preventing imbalance and decay. Like patient custodians, they maintain the continuity of predation, ensuring that energy continues to flow up and down the food web even in the cold months (Prugh et al., 2009).

In their absence, the estuary might collapse inward — prey would overgraze, detritus would pile, and oxygen would vanish from the mud. But the dogfish, efficient and tireless, keep the waters breathing.

Crabs and Killifish Take the Stage

Blue crabs roam the winter marsh, feeding on detritus and benthic invertebrates. Their slow foraging helps recycle nutrients and sustain the estuary’s energy balance through the cold season.

Within the estuary itself, the smaller actors continue their work. By December, the New River’s mudflats and marsh creeks host a quieter cast — mummichogs (Fundulus heteroclitus), sheepshead minnows (Cyprinodon variegatus), and grass shrimp (Palaemonetes pugio). These resident species, often unnoticed, now carry the estuary’s metabolism on their backs.

They thrive on detritus and microbial mats, converting decay into new life (Kneib, 2015). Blue crabs roam like slow-moving janitors, shifting through sediment to feed on worms and organic matter (Kennedy & Cronin, 2007). Each movement releases trapped nutrients, fueling microbial blooms that will later nourish the first plankton of spring.

While the spiny dogfish patrol the edges of the continental shelf, these smaller species sustain the inner heart of the estuary. Their labor keeps the water alive long after the glamour of migration fades.

Nutrient Loops and Winter Stability

Without large predators, the estuary depends on microbial and detrital loops to keep its energy cycling. Up to 70% of carbon transfer between November and February occurs through benthic detritivory and microbial remineralization rather than direct predation (Friedrichs & Perry, 2001).

This invisible economy sustains the overwintering fish and crustaceans — the leftovers that, in time, will become the first meal of spring’s returning predators. It’s the estuary’s savings account: energy stored as biomass and sediment, ready to be withdrawn when the tides warm again.

When winter quiets the hunt, the estuary turns inward. Instead of predators driving the cycle, nutrients move through the mud itself — microbes and detritivores recycling what’s left behind. This unseen flow keeps the New River alive until spring’s return (adapted from Erler et al., 2020).

A Resilient Feast

By January, the estuary seems dormant to the casual eye, but beneath its glassy surface, life reorganizes with quiet precision. Crabs clean the table. Dogfish patrol the edge. Minnows and shrimp sift through the silt for remnants of summer.

The New River continues to breathe — slower, deeper, deliberate.
When the big fish return with the first warm tides, the table is set once more, and the energy once left behind has been transformed — recycled through countless small mouths and patient currents into the promise of another season’s chase.

References

Allen, D. M., Govoni, J. J., Able, K. W., Buckel, J. A., Hale, E. A., Hilton, E. J., Kellison, G. T., Targett, T. E., Taylor, J. C., & Walsh, H. J. (2024). Long-term dynamics of larval and early juvenile spot (Leiostomus xanthurus) off the U.S. East Coast: Relating ocean origins, estuarine Ingress, and changing environmental conditions. Fishery Bulletin, 122(4), 162-185. https://doi.org/10.7755/fb.122.4.3

Baird, D., Luczkovich, J., & Christian, R. (1998). Assessment of spatial and temporal variability in ecosystem attributes of the St marks national wildlife refuge, Apalachee Bay, Florida. Estuarine, Coastal and Shelf Science, 47(3), 329-349. https://doi.org/10.1006/ecss.1998.0360

Carlson, A. E., Hoffmayer, E. R., Tribuzio, C. A., & Sulikowski, J. A. (2014). The use of satellite tags to redefine movement patterns of spiny dogfish (Squalus acanthias) along the U.S. East Coast: Implications for fisheries management. PLoS ONE, 9(7), e103384. https://doi.org/10.1371/journal.pone.0103384

Clark, K. L., Ruiz, G. M., & Hines, A. H. (2003). Diel variation in predator abundance, predation risk and prey distribution in shallow-water estuarine habitats. Journal of Experimental Marine Biology and Ecology, 287(1), 37-55. https://doi.org/10.1016/s0022-0981(02)00439-2

Foster, S. Q., & Fulweiler, R. W. (2014). Spatial and historic variability of benthic nitrogen cycling in an anthropogenically impacted Estuary. Frontiers in Marine Science, 1. https://doi.org/10.3389/fmars.2014.00056

Friedrichs, C. T., & Perry, J. E. (2001). Tidal Salt Marsh Morphodynamics: A Synthesis. Journal of Coastal Research, (27), 7-37. https://www.jstor.org/stable/25736162

Kennedy, V. S., & Cronin, L. E. (2007). The blue crab: Callinectes Sapidus. Maryland Sea Grant College University of Maryland.

Kneib, R. T. (1986). The role of Fundulus heteroclitus in salt marsh trophic dynamics. American Zoologist, 26(1), 259-269. https://doi.org/10.1093/icb/26.1.259

Prugh, L. R., Stoner, C. J., Epps, C. W., Bean, W. T., Ripple, W. J., Laliberte, A. S., & Brashares, J. S. (2009). The rise of the Mesopredator. BioScience, 59(9), 779-791. https://doi.org/10.1525/bio.2009.59.9.9

November 29, 2025