Episode 22
Copyright © John Page Williams Jr. All rights reserved.
This is John Page Williams with another reading from Chesapeake Almanac. The month is August and the title of this chapter is "What Good Are Sea Nettles?"
"What use is a jellyfish to the Chesapeake?" That's a question most of us ask every summer, and with good reason. The animals are the nemesis of swimmers, board-sailors, water-skiers, and anyone else who spends time in the Bay's water. The colloquial name of jellyfish tends to change to sea nettle or stinging nettle in Virginia, but the creature is the same.
Our stinging nettle is broadly distributed throughout the Chesapeake. It seems to prefer mid-range salinities, so it's more abundant from Baltimore to the mouth of the York than at the extreme upper or lower ends of the Bay. Wet springs and heavy storms like tropical storm Agnes in 1972 seem to depress the population.
Sea nettles belong to the phylum Coelenterata, which includes corals and sea anemones. Coelenterates are primitive but highly successful. In all of them, from coral to nettle, the body is soft and jellylike, basically just a sack of digestive enzymes with a mouth ringed by trailing arms. The arms may be long or short, and the body may secrete a hard coating, as corals do, or remain soft. Some coelenterates feed on microscopic zooplankton, using rows of tiny waving hairs called cilia to move the food to the mouth. Most, however, are carnivorous. They have stinging cells called nematocysts on their tentacles to catch and paralyze prey like small fish. Once the prey are caught, the tentacles transfer them to the mouth. It's not uncommon to find a stinging nettle with a small silverside or bay anchovy "in its head."
Coelenterates that are sessile are stationary, like corals and anemones, have the body sac attached to a substrate (that would be a reef, an oyster shell, or some other firm base), while the tentacles wave above, catching prey that pass by. Sea nettles simply reverse the plan, drifting along with the sac above and the mouth and tentacles trailing below. For all coelenterates, this body stage is called the medusa, after the mythological creature with snakes for hair. They're simple animals. The mouth serves both to take in food and to eliminate wastes. There is some sense of touch, some chemical sense of taste and smell, and some light sensitivity.
Jellyfish movements are simple and coordinated by a nerve "net" without centralized control by a brain. Swimming, though graceful, is very slow. Jellyfish are, in fact, planktonic. That is, they drift with wind, tide, and other currents. Most kinds of plankton are tiny, but a few are large, and jellyfish are good examples of this latter group. In fact, because they are planktonic and delicate, they tend not to occur in areas with heavy wave action, especially around beaches. Those that do often smash to pieces.
It's worth remembering that nettles are planktonic when choosing a place to swim from a boat. Unless they're extremely thick, it may be possible to find an area in a creek or river from which the wind and tide have carried them away.
The sting of a nettle occurs when a nematocyst senses something touching it and fires out a barb. The barb is, in effect, a poisoned dart, with a fine filament attached to help the nettle grasp its prey. The dart is too small to penetrate thick skin, like the palms of human hands, which is why we can pick nettles up carefully by the sack, by the head. And the filaments are too small for humans even to be aware of, but the poison, which is a protein, is something else. In most people it causes an immediate stinging sensation, followed by a mild rash and an itch that may last 20 minutes. It's painful, but certainly not dangerous. Some people have little or no reaction. a few people experience a stronger rash with a headache, and the pain may persist for three or four hours. First aid consists of washing the affected area, rubbing sand on it (though this may have more psychological than physiological value), and applying meat tenderizer. The latter contains papain, a generalized enzyme that breaks down most proteins, so it is at least partially effective. For more serious reactions, aspirin may help. If symptoms persist for more than four hours, or go beyond a headache, see a doctor promptly. The jellyfish system of reproduction is unusual. A number of coelenterates, and some other plants and animals, go through a process called alternation of generations. Nettle medusas reproduce sexually in late summer and early fall. Males release sperm, which are taken in by females while feeding. Shortly after, they release larvae which swim to the bottom and attach there to live as sessile creatures called polyps. Each lives through the winter, forming the upper part of its body into a stack of disks. In the spring, the discs pop off one by one in what's called asexual reproduction. Each develops into a new medusa to haunt swimmers, skiers, and board-sailors the next summer, and then to continue the cycle. Thus there are none of the familiar nettles of our local species around in the winter.
There are, however, some other jellyfish in cold weather. The most common is the winter jellyfish. It's orange in color, and it does sting, but because there are a few people in the water then, especially with exposed skin, it is not so much of a problem as its summer cousin. Another species that shows up throughout the year, especially in the lower Bay, is the moon jellyfish, or four-leaf clover. It is large, up to two feet in diameter, with short two- to four-inch tentacles. The four-leaf clover nickname refers to the four round circles in its body that houses sex organs. The moon jellyfish is a plankton feeder, and its short tentacles are only a minimal hazard. It's more of a thing of beauty than a nuisance.
Sea nettles may irritate hundreds of people, but they're not a serious enough problem to attract research money. Some work was done on them in the 1960s, but it was aimed primarily at studying the biology of the animal, and it ended without addressing the idea of controlling them. For now, all we can do is keep on buying meat tenderizer, water skiing in long pants, and appreciating wet spring weather.
Find out more on our blog, "Four Surprising Facts About Chesapeake Jellyfish."
For more happenings around the Bay in August see our other Chesapeake Almanac podcasts and read our blog post "Late Summer Glory in Tidal Fresh Marshes."
