Bay Stingers

By Henry S. Parker

Pulsating bags of protoplasm known as sea nettles can mar the best midsummer day on the Bay. Anyone who ventures out from May to October risks stings from these pesky jellyfish. As their populations expand with rising water temperatures, even a quick dip in the Chesapeake could send swimmers fleeing to shore. Fortunately, there are ways to avoid being stung — and remedies if it does happen.

Sea nettles (Chrysaora chesapeakei) might look like simple creatures but they’re voracious predators with lots of moving parts. Some two dozen tentacles drape from a transparent, umbrella-shaped, 4-inch bell known as the medusa. The tentacles contain nematocysts — barb-like stinging cells that discharge venom when encountering prey, predators, or unwary humans — and ensnare and paralyze small fish and animal plankton. The nettle then transfers the capture to its mouth, located directly under the bell’s center. 

Though seemingly unappetizing, sea nettles feed many larger species including sea turtles, fish, and crustaceans. The jellyfish are 90 percent water, so it takes a lot of them to sate a predator’s appetite. But, especially in midsummer in Chesapeake Bay, the waters teem with sea nettles. Midsummer also marks their spawning season. Females pump sperm-laden water through their bodies, fertilizing eggs that develop into free-swimming larvae. The adults then die as the larvae settle onto surfaces. There the larvae become polyps which give rise to floating medusae. The medusae grow into adults and the cycle begins again.

Sea nettles thrive in the brackish, warm waters of Chesapeake Bay but they’re not the only stinging species in the estuary. The Bay is also home to Moon Jellies, twice the size of nettles (their sting isn’t harmful to humans), and the Lion’s Mane Jellyfish whose sting is powerful but which, fortunately, only shows up in winter. The common and ecologically important “comb jellies” (ctenophores), a favorite food of sea nettles, are not true jellyfish. 

We can be thankful that the Bay doesn’t harbor Box Jellyfish, the world’s deadliest marine animal. Native to Australia and Southeast Asia, they’re responsible for dozens of human deaths every year. A single box jellyfish carries enough poison to kill up to sixty people in two minutes. 

That is not to diminish the discomfort of sea nettle stings. Severe stings can even be life-threatening to children or other vulnerable individuals. So it’s best to avoid them by staying out of the water during their peak summer season. To track their abundance, the geeks among us might want to follow NOAA’s daily sea nettles map for Chesapeake Bay (Sea Nettles Probability of Encounters (Experimental) (weather.gov). If you do get stung, you can choose from several remedies including applications of baking soda, hydrocortisone creams, shaving lotion, or meat tenderizer. First rinse the affected area with Bay water (not fresh water). Experts discourage applying vinegar — or urine.

No doubt, sea nettles are … well, nettlesome. So what good are they? They play an important role in the Bay’s ecology. They’re a significant source of food for many larger species. They eat a lot of ctenophores which are major consumers of oyster larvae. They’re a good indicator of the health of the Bay. But, like other indigenous species in the Bay’s food web, an imbalance in their numbers can disrupt the entire ecosystem. Sea nettles can become too much of a good thing.

This may already be happening. Jellyfish populations are expanding around the world, including in Chesapeake Bay. University of Maryland scientists point to two factors: increasing nutrient levels that fuel algae blooms and, in turn, more prey for sea nettles; and overfishing — depleted seafood stocks free up more food for jellyfish. In turn, more hungry nettles mean less feed for other species. And rising water temperature from climate change stimulates nettle population growth earlier in the season. Ultimately, the Bay’s water quality will determine the future fate of sea nettles, as it does for other Chesapeake denizens. 

Sea nettles will never become Bay fan favorites, but they’re important and fascinating creatures. So do take some time to get familiar with them. Just not too familiar.

Henry (“Hank”) Parker is a scientist and writer who previously lived in Annapolis but now lives in Vermont.