By M. Kathy Raines
Special to the PRESS
A freckled, five-inch gelatinous blob lay among clumps of sand at Isla Blanca Park one recent June afternoon. “Look! What is that?” cried my alert sister. We’d never seen this creature.
We customarily weave around the lovely azure and pink balloons—and long, stinging tentacles—of Portuguese men-of-war, and we avoid sliding on the slippery, translucent bells of sometimes countless moon jellyfish dotting our shores. But we’d never seen this jellyfish, the Atlantic bay nettle, and thank goodness we didn’t touch it, for it packs a powerful sting.
The Atlantic bay nettle (Chrysaora chesapeakei), along with moon and lion’s mane jellyfish and fellow nettles, in the class Scyphozoa, is considered a “true jelly”. Its scalloped bell contracts to propel itself through the water. About 40 tentacles—armed with nematocysts, or venom-packed capsules—fringe the bell. When triggered, these stinging cells uncoil and, harpoon-like, pierce shells and skin, injecting venom. Aquatic nettles, all of which deliver a bee-like sting, are named after flowering plants whose leaves and stems harbor hollow stinging hairs.
Four long, plumy “oral arms”, like feathered boas, trail from the bay nettle’s multi-purposed mouth—an orifice that not only ingests food but also serves to expel wastes and release or capture sperm. As this jellyfish pulses, it creates a current which pushes its prey—including zooplankton, larvae, small crabs and fellow jellyfish—within its tentacles and outspread arms, also envenomed. Assisted by a coating of hairlike cilia, the arms insert food into the nettle’s mouth. Though a nettle lacks a centralized brain, it has sensory structures that can detect light, gravity and water chemistry.
Until 2017, biologists grouped the bay nettle and the Atlantic sea nettle (Chrysaora quinquecirrha) into the latter species, but DNA evidence has shown that the bay, though similar in appearance, is more closely akin to faraway species of nettles, some from Ireland, Argentina and the African coast. With a bell about half the size of an Atlantic sea nettle’s, the bay nettle has longer arms but fewer tentacles. It also lives closer to shore and can thrive in lower salinities.
Bay nettles inhabit brackish coastal waters of the Atlantic and Gulf coasts. Jennifer Broywen, Program Coordinator at the UTRGV Coastal Studies Laboratory, reported that the nettles “are often washed ashore along the beach and bay areas, especially during the warmer summer months when they are more abundant in coastal waters.” In summers, she said, people commonly “find them stranded on the shoreline” since “tides, currents and wind can carry them into shallow waters and eventually onto land.”
In summertime, a male nettle discharges sperm, which a female sweeps into her mouth. She carries the fertilized eggs on her arms until they transform into planulae, or tiny, cilia-coated larvae. These swim off and, after a few days, cement themselves to a hard surface, often a shell or rock, but sometimes a dock or boat. Here they turn into polyps, tiny anemone-like creatures that, armed with stinging tentacles, devour plankton and, under favorable conditions, reproduce. A polyp buds off, cloning itself, and creates a stack of disc-like offspring. One by one, from the top down, each swims away as an ephyra, or larva which, within weeks, becomes a medusa, or adult jellyfish. When food or oxygen is scarce or waters too warm, polyps shrink to cyst-like creatures called podocysts that can survive, sometimes for years, until circumstances improve.
Juvenile crabs, often spider crabs or young blues, may inhabit a bay nettle’s bell, scrubbing out parasites and debris. Some nudibranchs (sea slugs) eat jellyfish, using their pilfered stinging cells to enhance their own hunting.
Obviously, swimmers and divers do not welcome venomous nettles, yet these creatures are vital to the food web. For example, comb jellyfish consume lots of oyster larvae, but bay nettles particularly relish eating these jellyfish, thus allowing more oysters to thrive. Bay nettles appear to be hardy survivors. A study of those living in the Chesapeake Bay revealed them to be relatively insensitive to oxygen depletion in water.
A bay nettle’s sting is neither as intense nor as enduring as that of a Portuguese man-of-war, and swimmers may more easily avoid the nettle’s tentacles, which extend a few feet, to a man-of-war’s 30 to 100. Still, a nettle’s sting causes sharp, burning pain and can raise sometimes blistering welts. Systemic symptoms like nausea, vomiting, cramps, weakness and headache—often due to allergic reactions—do warrant medical attention. Experts recommend rinsing the skin with sea water, extracting visible tentacles (while protecting one’s hands) and dousing it with warm water or applying a warm compress. Many also recommend applying vinegar.