Jellyfish are abundant along the Georgia coast. These pulsing bells are among the most primitive animals on earth. Their simple nervous system lets them detect and capture prey with tentacles loaded with nematocysts, specialized stinging cells that discharge long threads full of toxic venom when the tentacles encounter a potential meal. Jellies with circular bells are the familiar ones featured in riveting displays in marine aquariums. Watching as the alternately contracting and expanding bells trailing long tentacles circulate up and down in the tanks is a Zen-like experience, as meditative as staring at rising and falling blobs in lava lamps.
Photo above of jellyfish in an exhibit at the Monterey Bay Aquarium. By Omegacentrix (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
On the other hand, box jellies, with gelatinous bodies that are cubic rather than round, are rarely kept in aquaria, for good reason. Box jellies are incredibly venomous. These transparent jellies, although generally smaller than their bell-shaped kin, are strong swimmers, can travel at rates of up to eighteen feet a minute, and have complex eyes, complete with lenses and retinas. Their visual acuity and speed make them active hunters of small fish. Their potent toxins stun their struggling victims into quick submission. The famous box jellies that swarm off the eastern and northern coasts of Australia cause agonizing stings that have even killed badly stung swimmers by causing cardiac arrest in a matter of minutes. Recent reports of people experiencing symptoms of box jelly stings off Florida, as in this National Geographic documentary, Attack of the Giant Jellyfish, are ominous.
Photo of a sign on a beach in northern Australia warning swimmers of the dangers of box jellyfish. Taken by E. Sherr during a 2011 birding trip.
The simple body plan of gelatinous zooplankton suggests that these animals evolved early in earth's history. Indeed, the fossil record shows that jellyfish were among the first animals to appear in marine plankton. Since they don't have bones or shells, jellyfish are not easily detected in ancient rocks. Fortunately, animals that died and fell into soft marine muds often left impressions of their bodies in mudstone formations. In 2007, Paulyn Cartwright, a professor at the University of Kansas, reported that she and her colleagues had discovered beautiful fossil imprints resembling modern jellyfish, complete with bells and tentacles, in mudstone deposits in Utah dated to the middle Cambrian, 505 million years ago. Oceanographers who study the geological history of the sea call this primordial period the "jellyfish ocean," since these creatures were the top predators in the plankton before the appearance of fish.
There is now serious worry that the ocean is returning to a jellyfish dominated state. (The excellent, but unnerving, book Stung! On Jellyfish Blooms and the Future of the Ocean, by Lisa-ann Gershwin, details this concern). Outbreaks of jellyfish swarms have been alarming fishermen and beachgoers in recent years.
One of the most amazing developments has been the proliferation of the giant jellyfish, Nemopilema nomurai, in the China Sea. The bell of this enormous jelly grows up to seven feet across, and a large specimen can weigh several hundred pounds. First identified in 1921 by a Japanese fisheries researcher, Kanichi Nomura, until recently this species was a marine curiosity. Lately, however, vast swarms of Nomura's jellyfish have been migrating from their traditional habitat in the warm China Sea up the coast of Japan during summer. Considering the weight of just one of these monsters, it is no wonder that the nets of fishing boats are clogged and broken by these jellies.
These and other exceptional jellyfish blooms are thought to result from of a combination of sea surface warming due to climate change and the overharvesting of fish that are jellyfish predators and competitors for plankton food. Both warmer waters and fewer fish would boost jellyfish numbers, and these simple, brainless bags of goo are eating machines that can grow like crazy when they get a chance. It might be, though, that jellyfish go through natural boom-and-bust cycles, so the scientific jury is still deliberating whether these creatures are going to retake the sea.
It is just as well that the enormous, net-busting Nomura's jellyfish doesn't live off the Georgia coast!
Although no deadly or giant jellies occur in southeastern estuaries, many species of these primitive animals are found here. Two species of stinging jellyfish are especially common. The lion's mane jelly, Cyanea capillata, has a pinkish-red umbrella, or bell, with frilly tentacles in eight separate clusters, and is most abundant during colder winter months.
The other common stinging jelly is the appropriately named sea nettle, Chrysaora quinquecirrha, which has a thick flat bell, up to six inches across and white to reddish brown in color, with about twenty tentacles hanging from the margins. Sea nettle tentacles are loaded with nematocysts, and this species is a voracious predator of zooplankton and larval fish. Unlike the lion's mane, the sea nettle jelly prefers warm water and can tolerate brackish salinities which allows it to thrive in estuaries and up river mouths. During summer, sea nettles are abundant along the Georgia shore. Researchers diving at Gray's Reef, a hard-bottom habitat which is a National Marine Sanctuary several miles offshore from Sapelo Island, have reported such dense concentrations of nematocyst-laden sea nettles and other jellies that they could not avoid being constantly stung. They are also a danger for swimmers at the beach. Sea nettle tentacles break off in the surf, so that even when jellyfish bells are nowhere in sight, a painful sting can be delivered by an unseen free-floating tentacle. Jellyfish washed up on the sand can zap a toe or finger.
The recommended treatment for a jellyfish sting is to wash the affected area with saltwater, not freshwater, since freshwater will cause the nematocysts to release more toxins.
"Stomolophus meleagris". Licensed under Attribution via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Stomolophus_meleagris.jpg#/media/File:Stomolophus_meleagris.jpg
One of the largest jellyfish along the southeastern US coast is the cannonball, Stomolophus meleagris. Locals call them "jellyballs." Unlike its flimsier cousins, the cannonball has a very firm, pinkish-white bell, up to a foot in diameter, with a mass of tentacles protruding from the bottom. When discharged, cannonball nematocysts are shorter than those of the lion's mane or sea nettle, so they can't penetrate human skin very well. I nonetheless managed to get stung once by a cannonball. Leaning far over the front end of a Boston whaler to scoop one out of the water, I toppled over and found myself face-to-bell with it. I felt a slight stinging around my eyes, but that was all. Young spider crabs often hitch a ride on these big jellies, finding shelter and free meals until they are large enough to compete with adult crabs on the sea bottom. The juvenile crabs stay with their host even when the jellyfish is washed up onto the beach. When I picked up one cannonball from the surf, no less than five inch-long spider crabs were crawling around inside the bell.
On research cruises off the Georgia coast, I have seen row after row of thousands of cannonballs pulsing along the surface. To fishermen, the cannonball jellies are a nuisance. During the summer, the abundance of cannonballs is so high that shrimpers' nets become clogged with them. Their trawls are so often fouled with the big jellyballs that they have been forced to add mechanical "jellyball shooters" to their nets to shunt them out of the way.
But one clever fisherman knew that dried jellyfish was a delicacy in China and Japan. He decided to set up a cannonball processing plant in Darien, a fishing port on the Altamaha River. By the early 1990s, shrimp fisheries along the Georgia coast had become less profitable because of a flood of cheap imported farmed shrimp. Catching and processing jellyballs for export had the potential to supply a niche market, possibly bringing in more money than shrimp trawling. The jellyfish-processing plant in Darien has been operating ever since. The cannonball jellies are easy to catch by slow trawling. Once delivered to the factory, the bells of the jellies are dried, packaged, and shipped out to Asian countries. So far, there is not much demand in the United States for dried jellyfish. But jellyballs are currently the third-largest fishery product, by weight, in Georgia.