Neither Jelly nor Fish
The stinging jellyfish which makes the Chesapeake Bay so inhospitable in the summer is the sea nettle, Chrysaora quinquecirrha. While sea nettles occur from Cape Cod south along the U.S. East Coast, Caribbean and Gulf of Mexico they inhabit the Bay in numbers unequaled elsewhere. They are found most abundantly in the tributaries of the middle Bay where salinities are between 10 and 20 parts per thousand. At those salinities, they are white in color. In the southern Bay, where salinities are higher, they often have red/maroon markings on the long central tentacles and on the swimming bell, or medusa.
The Sting: Prevention and Treatment
The tentacles of the sea nettle contain millions of microscopic stinging cells called nematocysts that inject toxins to capture and paralyze prey as well as to defend the jellyfish from would-be predators. When a swimmer brushes against a tentacle, the resulting sting is painful and annoying. Lightweight protective clothing, like a Lycra "swim skin" or panty hose, or a layer of petroleum jelly spread on bare skin will protect a swimmer against stings.
There are several things that you can do if you get stung. If bits or pieces of tentacles are still on the skin, pour alcohol or baby powder on the area. Alcohol will stabilize the nematocyst so that it will not be triggered. Powders do the same by drying the cells out. Without such treatment, tentacles which are disturbed may release additional nematocysts, causing additional irritation and swelling.
Next, apply diluted ammonia, sodium bicarbonate, vinegar or meat tenderizer to the area to relieve pain. Meat tenderizer is one of the best sources of relief from stings. Add a small amount of water to the meat tenderizer to make a paste and smear it on the inflamed area. Meat tenderizer is an enzyme which breaks down proteins. Jellyfish venom is made of protein and is consequently destroyed by the meat tenderizer.
Few Predators, No Good Controls
The sea nettle is unusual in its ability to live in low salinity water. Most jellyfish species live at ocean water salinity, about 35 parts per thousand, while the sea nettle prefers waters with as little as 12 parts per thousand salinity. This means that it usually has estuaries like the Chesapeake Bay to itself without serious competition from most other jellyfish. In fact, sea nettles eat their most abundant competitors in the Bay, comb jellies, or ctenophores.
Adult sea nettles have few natural predators in the middle reaches of the Chesapeake Bay. Sea turtles, which are known to eat Portuguese man-of-war and some other jellyfish, rarely come far into the Bay. And fish species (harvestfish and butterfish) observed feeding on sea nettles prefer waters of higher salinity.
A lot of effort was spent on jellyfish control in the Bay in the 1960s, but no method was very successful. Nets and bubble screens were used to keep them away from swimming areas. The jellyfish tended to clog the nets and to break into pieces that continued to sting. The bottomliving polyp stage also was targeted. Chemicals that killed the polyps also killed many other organisms, and so were unsuitable. Researchers found a small species of sea slug that ate polyps, but culture methods to produce large numbers of the sea slugs were unsuccessful and they also did not live well at the low salinities favored by the polyps.
The only thing known to reduce jellyfish populations is an influx of fresh water. Experiments have shown that sea nettles reproduce poorly at less than 7 parts per thousand salinity. Hurricane Agnes in 1972 caused the greatest reduction of jellyfish populations in recent years.