By Hank S. Parker

            Admit it. You won’t take a dip in the Chesapeake Bay after mid-June. Not because of rampaging jet skiers, pollution-spawned flesh-eating bacteria or errant sharks. All scary enough, if remote risks. Your real fear is of getting stung by the Bay’s most loathsome creature: the sea nettle.

Sea nettles are jellyfish. They show up here in May, hang around until October or so, and are most abundant, especially in the middle Bay, in mid-summer. They look like semi-transparent saucers laced with mahogany-colored stripes and speckled with small white dots. On their undersides, by their mouths, four oral arms hang down. Up to two dozen tentacles, which may be several feet long, dangle from the animal’s periphery. The main body of the jellyfish—its bell—is normally about four inches in diameter, but may grow to the size of a large soup bowl.

At 95 percent water, there isn’t much substance to a sea nettle. But they make the most of their scanty protoplasm, especially when it comes to reproducing. During the summer, males and females discharge sperm and eggs, some 40,000 a day. Fertilized eggs become larvae that attach to hard surfaces. Larvae develop into tiny knob-like polyps that winter on the Bay bottom. During spring and summer, polyps pinch off miniature floating discs that quickly grow into fertile, adult forms known as medusae.  A single polyp can produce 45 fully-grown jellyfish.

A medusa can weakly propel itself through calm waters by rhythmically contracting its bell. But sea nettles, like all jellyfish, are plankton, meaning they drift at the mercy of currents and winds.

Sea nettles prefer brackish water (a mix of fresh and salt) and temperatures of between 78 and 86 degrees Fahrenheit. Because these conditions typify the middle and lower Chesapeake Bay in the summer, sea nettles are more numerous in these waters than anywhere else on earth. When the environment is unfavorable—such as after a hurricane when copious rainfall greatly lowers the Bay’s salt content—polyps can remain dormant, ensheathed in cysts, until conditions improve.

Killer Jellyfish?

If a sea nettle stings you, you won’t soon forget it. The sensation, described variously as prickly, burning or paralyzing, is bee sting painful. In rare cases, the venom can cause a dangerous allergic reaction. But sea nettles, unlike their notorious cousins, the box jellyfish, are not lethal. Good thing box jellyfish don’t live in the Bay. That Indo-Pacific species has killed more than 5,000 people in the past half century.

Sea nettles aren’t even the most annoying jellyfish in Chesapeake Bay. That distinction belongs to the Lion’s Mane Jellyfish whose sting is worse than the sea nettle’s and whose tentacles, in North Atlantic waters, can grow to more than 100 feet long. But the Lion’s Mane prefers cold waters, and inhabits the Bay only in winter. The other common local jellyfish, the Moon Jelly, has a comparatively mild sting.

If You Get Stung

Know your enemy. Good advice, even if the foe is a sea creature. In the case of sea nettles, it helps to understand their weapon systems.  Sea nettles, like all jellyfish, corals and sea anemones, are armed with stinging cells. These cells, known as nematocysts, are arrayed along the animal’s tentacles and oral arms, and are used in feeding or as a defense against predators. Each capsule-like nematocyst encloses a tightly coiled, barbed thread. When tentacles contact a firm object, like prey or an unwary swimmer, the nematocysts discharge, firing toxin-laden, harpoon-like threads into the victim. You would just feel a sting; a minnow would be paralyzed and quickly consumed.

Short of layering yourself with panty hose or petroleum jelly, there isn’t much you can do to avoid getting stung if you swim with sea nettles. So what to do if you’re a victim? You could simply live with the pain. It should subside in a half hour or so. But if it’s intolerable, and you just happen to be packing meat tenderizer or baking soda, you can apply this to the affected area. Some grizzled fishermen recommend urinating on the wound, which would be admittedly difficult if the nettle gets you in the back. Would it work? The scientific jury is still out.

But a new antidote has come to the rescue: Jellyfish Squish. Endorsed by the American Lifeguard Association and complying with U.S. Food and Drug Administration standards, the product (the formulation is a trade secret) reputedly numbs the pain when sprayed on the sting site.

What Good are Sea Nettles?

Although humans may not like them, sea nettles have long been an integral part of the Bay’s ecosystem. They chow down on animal plankton, especially abundant, microscopic copepods. This may help the Bay’s water clarity. It has also been suggested that sea nettles aid the Bay’s oyster populations by consuming comb jellies, the major predator of oyster larvae. Not much will eat sea nettles. Even if a potential predator could deal with the stinging threat, it wouldn’t find much nutrition in the gelatinous blob. But sea turtles are fond of jellyfish and loggerheads also prey on Chesapeake Bay sea nettles.

Henry S. (“Hank”) Parker has been a U.S. Naval officer, deep-sea diver, seaweed farmer, marine biologist, university professor and research director for the U.S. Department of Agriculture. Now focusing on teaching and writing, he lives in Annapolis with his wife, Sue, and can be contacted at [email protected]

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