Sharks of Onslow County
Several species of jellyfish appear along the waters of Onslow County, North Carolina as the coastal ecosystem shifts from winter toward spring. Moon jellies, comb jellies, sea nettles, and cannonball jellyfish all move through these waters at different times of year, responding to temperature, tides, and the seasonal return of plankton (Purcell et al., 2007; Lucas et al., 2012; Cloern & Jassby, 2010).
In late February along the Intracoastal Waterway, the coast exists in a kind of suspension. The marsh grasses behind Topsail Island are still the color of dried straw, their green not yet returned. The wind carries more memory than warmth, and the water — though brighter in the lengthening light — remains clear in the way cold water often is, revealing sandy bottom, oyster shell, and shadow without the haze of summer plankton.
Nothing looks abundant. Nothing appears urgent. The shoreline feels patient.
If you lean over a dock and allow your eyes to adjust, the surface begins to resolve into layers. What first appears empty reveals movement — a faint pulse beneath the water, nearly invisible unless sunlight strikes at the right angle. A small translucent bell, no wider than your palm, opens and closes in a steady rhythm while the current carries it sideways through the creek.
The first jellies of the season are easy to miss.
They are small.
They are clear.
And they belong to the quiet phase of the coastal year.
Early spring water along the southern North Carolina coast often carries a glass-like quality. Plankton populations are rebuilding after winter. Suspended sediments have settled during calmer stretches. Against that clarity, the earliest gelatinous drifters seem almost designed to disappear.
Standing along the docks and creeks of Onslow County, most of what we notice are the drifting bells moving slowly through the water.
But the life of a jellyfish does not begin there.
The jellyfish most people recognize — the drifting bell, the trailing tentacles — is only one phase of a much longer life cycle.
Most true jellyfish begin as fertilized eggs released into the water column. Each egg develops into a tiny, free-swimming larva called a planula. There are many planulae in the water at once, but each one is a single organism, smaller than a grain of sand, carried by currents you would never notice from the surface.
Within a few days — sometimes less than a week, depending on temperature — a planula settles onto a hard surface. It may attach to the underside of a dock piling, the rough edge of an oyster shell, a shaded bridge support, or even a shell resting quietly in the mud. Once attached, it transforms into a polyp (Lucas et al., 2012).
In this stage it does not resemble a jellyfish at all. It is small — often only a few millimeters tall — no larger than a grain of rice. If you could flip that piling into the sunlight in February, you would not see a jellyfish.
You would see something that looked more like a pale freckle against the wood.
And yet, that freckle holds potential.
The polyp may remain in that form for months. Anchored beneath docks and along oyster beds, it feeds on microscopic prey drifting past and survives the colder stretch of winter water (Purcell, 2012).
That freckle — that rice-sized polyp — does not always remain alone.
In some species of true jellyfish, the polyp stage can reproduce asexually, forming small copies of itself along the same piling or oyster shell (Purcell, 2012).
When spring begins to soften the creek and temperatures rise, the polyp changes again. In a process known as strobilation, its body reorganizes into stacked segments (Purcell et al., 2007; Lucas et al., 2012). One by one, those segments separate into the water as tiny juvenile jellyfish called ephyrae (Purcell et al., 2007).
As the ephyra develops, its arms fill in and smooth into a rounded bell. It becomes the drifting medusa we recognize along docks, tidal creeks, and open shoreline.
If you step away from the dock and look toward the darker center of the creek, the pattern shifts without breaking. Not every gelatinous drifter begins life attached to wood or shell. Comb jellies live their entire lives suspended in open water, developing and reproducing where freshwater flowing downriver meets saltwater moving inland on the tide (Purcell et al., 2001).
What can seem like separate coastal experiences — the pale freckle beneath a dock, the first small jellies of spring, the sudden sting beneath a swimsuit — are phases of the same unfolding life cycle.
Watch a jellyfish long enough drifting beneath a dock or through the calm water of a tidal creek in Onslow County, and the question eventually arises.
What is directing it?
The bell contracts. The animal pulses forward. Tentacles drift outward and close around passing prey. The movement appears deliberate, almost rhythmic, as though some quiet decision were being made.
And yet, jellyfish have no brain.
Instead, their bodies are organized around a diffuse network of nerve cells known as a nerve net. Sensory information travels across this web of neurons distributed throughout the bell and tentacles — more like signals moving along a strand of Christmas lights, where each bulb responds along the line, rather than a single switch controlling everything at once (Mackie & Meech, 1995).
Along the margin of the bell, specialized sensory structures known as rhopalia help them sense orientation and balance in the water column. In a way, they function a bit like the balance sensor in a phone that knows when the screen should rotate (Garm et al., 2006; Skogh et al., 2006).
None of these signals pass through a central command center.
Instead, the entire body participates in sensing the surrounding water.
The current shifts.
Light filters through the surface.
Something brushes against the tentacles.
And the jelly responds.
A moon jelly drifting beneath a dock in early spring may be only a few inches across. Its bell is nearly colorless, soft at the edges, its body so transparent that it seems less like an animal and more like a moving lens in the water.
What often gives it away are four faint circles inside the bell — pale rings that resemble small moons suspended within the jelly. Those structures are reproductive organs, and they are the feature that gives the species its common name.
Around the margin of the bell hang delicate, hair-fine tentacles. They are far shorter and less conspicuous than the trailing threads of sea nettles that appear later in the summer.
Earlier in its life it exists as a tiny polyp attached beneath docks and oyster shells — the same pale “freckles” that persist quietly through the winter on the shaded structures below the waterline.
As the water slowly warms into the upper 40s and 50s °F (8–13°C), those anchored moon jelly polyps begin releasing young jellyfish into the creek in a process scientists call strobilation (Purcell et al., 2007; Purcell, 2012).
As these young jellies drift through the creek, their bells pulse slowly against the current. The water around them carries clouds of microscopic life — copepods and other plankton rebuilding after winter — and whatever brushes the tentacles becomes food (Lucas et al., 2012; Cloern & Jassby, 2010).
Their tentacles do carry stinging cells, called nematocysts, like microscopic harpoons built to capture animals far smaller than we are. For most people, those harpoons are too small to penetrate the outer layer of human skin.
A swimmer may brush past a moon jelly without feeling anything at all.
Comb jellies — ctenophores such as Mnemiopsis leidyi — are even more elusive.
They lack stinging cells and instead capture prey with sticky cells (Purcell et al., 2001). Their bodies are almost entirely transparent. What gives them away are rows of tiny beating cilia that catch the light and flash briefly like moving prisms.
In darkness, some comb jellies can also produce brief flashes of bioluminescent light when disturbed, though along the creeks of Onslow County what we usually notice are the shifting rainbows created as sunlight bends through their beating cilia.
Unlike moon jellies that may first appear near docks and pilings, comb jellies are often more noticeable in slightly deeper portions of tidal creeks and open estuary as spring advances (Purcell et al., 2001).
From the dock, they can be invisible.
But scoop a bucket of water in late spring or early summer and the illusion changes. What looked like empty creek water suddenly fills with small gelatinous spheres — clear, bead-like forms tumbling gently against one another, not unlike the soft water beads children play with, often called Orbeez.
In a net, they resemble scattered jelly stones.
They have been there all along.
The difference is scale and perspective.
By late spring another gelatinous presence begins to make itself known, though most people never see the organism responsible.
On calm, warm days along the beach, swimmers sometimes step from the water with a faint prickling sensation along their skin. The irritation may begin around the ankles, between the toes, or beneath a swimsuit where fabric presses against the body. Hours later a rash can appear.
Locally this irritation is often called “sea lice,” though the name is misleading. They are not lice at all. The sensation comes from microscopic cnidarians — most commonly the larval stages of the thimble jellyfish (Linuche unguiculata), though larvae of certain sea anemones can produce the same reaction (Segura-Puertas et al., 2001; Wong et al., 1994).
At this stage the animals are nearly invisible, drifting in the surface water. Waves and gentle onshore currents can concentrate them along the shoreline, the same shallow areas where swimmers enter the water, children play in the surf, and beachgoers wade while searching for shells.
When these larvae become trapped against the skin — beneath fabric or pressed between toes and folds of skin — the same microscopic harpoons, or nematocysts, used to capture prey can inject a tiny amount of venom when triggered (Wong et al., 1994).
Most people recognize the sudden prickling sensation immediately. In the hours that follow, the irritation can intensify into a fiery rash — a reaction known medically as seabather’s eruption. Relief usually begins by rinsing the skin with fresh water after leaving the ocean and applying cold compresses to calm the irritation (Wong et al., 1994).
Few people ever see the organism responsible.
Spring along the coast rarely arrives all at once. It unfolds in stages — water warming by degrees, plankton building slowly in the creeks and sounds, and the community of gelatinous drifters shifting with those changes.
The nearly invisible jellies of early spring give way to species that are easier to see, easier to avoid, and sometimes easier to feel.
By late spring and early summer, the Atlantic sea nettle (Chrysaora quinquecirrha) begins appearing more frequently in the creeks and sounds of Onslow County.
Their bells carry warm amber tones, and long tentacles trail behind them like threads drifting through the tide.
Sea nettles favor the brackish mixing zones of the estuary where freshwater flowing down the New River blends with saltwater entering through the inlets. As plankton populations increase with warming water, sea nettles follow the food supply into tidal creeks and quieter sounds (Lucas et al., 2012).
Unlike moon jellies, their nematocysts can penetrate human skin, producing the sharp sting swimmers learn to recognize.
Farther offshore another species sometimes appears — the cannonball jellyfish (Stomolophus meleagris).
Their rounded bells give them the appearance of pale drifting mushrooms or underwater buoys.
They often gather in offshore waters where ocean currents concentrate plankton (Graham et al., 2003). Storms and onshore winds can push them toward the beaches of Onslow County, where they sometimes appear along the wrack line.
Many stranded individuals are no longer alive. Their gelatinous bodies collapse quickly once they leave the buoyant support of seawater.
Beyond the breakers, however, they may still be drifting quietly through deeper currents.
It is easy to think of jellyfish as modern phenomena — summer nuisances or passing curiosities.
Yet their lineage stretches back more than 500 million years, predating vertebrates and surviving multiple mass extinctions (Cartwright et al., 2007).
Long before barrier islands formed and migrated, eastern North Carolina lay beneath shallow marine waters.
Soft-bodied drifters pulsed through plankton-rich seas above what would eventually become Onslow County.
The small jelly beneath a dock in March is not something new.
It is continuity.
Stand again at the edge of the sound as winter begins to loosen its hold on the coast.
The air is softer now. Ospreys circle overhead. Marsh grass prepares to green.
Beneath the surface, the water is changing too — warming slowly, plankton returning, currents carrying new life through the estuary.
A small bell pulses quietly past the pilings. Nearby, comb jellies flash faint rainbows when the light strikes them just right. Somewhere beyond sight, larvae drift through the tide.
None of it announces itself.
But if you lean over the water long enough in early spring, you can watch the system beginning again.
Cartwright, P., Halgedahl, S. L., Hendricks, J. R., Jarrard, R. D., Marques, A. C., Collins, A. G., & Lieberman, B. S. (2007). Exceptionally preserved jellyfishes from the Middle Cambrian. PLoS ONE, 2(10), e1121. https://doi.org/10.1371/journal.pone.0001121
Cloern, J. E., & Jassby, A. D. (2009). Patterns and scales of phytoplankton variability in estuarine–coastal ecosystems. Estuaries and Coasts, 33(2), 230-241. https://doi.org/10.1007/s12237-009-9195-3
Garm, A., Ekström, P., Boudes, M., & Nilsson, D. (2006). Rhopalia are integrated parts of the central nervous system in box jellyfish. Cell and Tissue Research, 325(2), 333-343. https://doi.org/10.1007/s00441-005-0134-8
Graham, W. M. (2001). Size-based prey selectivity and dietary shifts in the jellyfish, Aurelia aurita. Journal of Plankton Research, 23(1), 67-74. https://doi.org/10.1093/plankt/23.1.67
Graham, W. M., Pagès, F., & Hamner, W. M. (2001). A physical context for gelatinous zooplankton aggregations: A review. Jellyfish Blooms: Ecological and Societal Importance, 199-212. https://doi.org/10.1007/978-94-010-0722-1_16
Lucas, C. H., Graham, W. M., & Widmer, C. (2012). Jellyfish life histories: Role of polyps in forming and maintaining Scyphomedusa populations. Advances in Marine Biology, 133-196. https://doi.org/10.1016/b978-0-12-394282-1.00003-x
Mackie, G. O., & Meech, R. W. (1995). Central circuitry in the jellyfish Aglantha Digitale: I. The relay system. Journal of Experimental Biology, 198(11), 2261-2270. https://doi.org/10.1242/jeb.198.11.2261
Mackie, G. O., & Meech, R. W. (1995). Central circuitry in the jellyfish Aglantha Digitale: II. The ring giant and carrier systems. Journal of Experimental Biology, 198(11), 2271-2278. https://doi.org/10.1242/jeb.198.11.2271
Purcell, J. E. (2012). Jellyfish and ctenophore blooms coincide with human proliferations and environmental perturbations. Annual Review of Marine Science, 4(1), 209-235. https://doi.org/10.1146/annurev-marine-120709-142751
Purcell, J. E., Shiganova, T. A., Decker, M. B., & Houde, E. D. (2001). The ctenophore Mnemiopsis in native and exotic habitats: U.S. estuaries versus the Black Sea basin. Hydrobiologia, 451, 145-176. https://link.springer.com/article/10.1023/A:1011826618539
Purcell, J., Uye, S., & Lo, W. (2007). Anthropogenic causes of jellyfish blooms and their direct consequences for humans: A review. Marine Ecology Progress Series, 350, 153-174. https://doi.org/10.3354/meps07093
Segura-Puertas, L., Ramos, M. E., Aramburo, C., Heimer de la Cotera, E. P., & Burnett, J. W. (2001). One Linuche mystery solved: All 3 stages of the coronate scyphomedusa Linuche unguiculata cause seabather’s eruption. Journal of the American Academy of Dermatology, 44(4), 624-628. https://doi.org/10.1067/mjd.2001.112345
Skogh, C., Garm, A., Nilsson, D., & Ekström, P. (2006). Bilaterally symmetrical rhopalial nervous system of the box jellyfish Tripedalia cystophora. Journal of Morphology, 267(12), 1391-1405. https://doi.org/10.1002/jmor.10472
Wong, D. E., Meinking, T. L., Rosen, L. B., Taplin, D., Hogan, D. J., & Burnett, J. W. (1994). Seabather’s eruption: Clinical, histologic, and immunologic features. Journal of American Academy of Dermatology, 30(3), 399-406. https://www.jaad.org/article/S0190-9622(94)70046-X/abstract
