Giant Jellies Invade Gulf of Mexico
By Hillary Mayell, National Geographic News, August 16, 2000
Scientists are working to determine whether an invasion of alien jellyfish into the Gulf of Mexico is an environmental disaster in the making, a new food crop that can be profitably harvested, or something in between. The spotted jellyfish, a native of Australia, first reached the Caribbean about 20 years ago, probably travelling as polyps on the hulls of ships coming through the Suez and Panama canals. Formally known as Phyllorhiza punctata, the jellies began arriving in the Gulf in June and are positively thriving in the nutrient rich waters of the Mississippi Sound. Typically 6 inches (15 centimeters) in diameter, they are reaching sizes of more than 2 feet (nearly 70 centimeters) across. "The magnitude of the invasion is unique, both in terms of the area invaded and the sheer numbers," says Monty Graham, a biological oceanographer at Alabama's Dauphin Island Sea Lab, speaking from the Pelican, a National Science Foundation research ship currently cruising in the Gulf. "The phyllo are phenomenally concentrated; in one area that we surveyed the other day they were actually bumping into one another every minute or so." The largest concentration of the gelatinous creatures is located off the coast of New Orleans, Louisiana, at the mouth of Lake Borgne. "There are easily a million," says Graham.
The current speculation is that the jellyfish made their way north by hitching a ride on the Loop Current (LC). The LC enters the Gulf of Mexico through the straits between Yucatan and Cuba, loops through the southeastern Gulf and then exits through the Straits of Florida. Satellite imagery shows that a big water mass broke off the Loop in early June into an eddy south of Alabama and the Florida panhandle. "This is a totally unusual biological event," says Harriet Perry, director of the Center for Fisheries Research and Development at the Gulf Coast Research Laboratory, who along with Graham, is heading an emergency response effort to get a handle on the invasion. "Everything was in place. The jellies were entrained in the water mass, there's a lot of plankton available to feed on now, the water is warm, and because of the drought, we have very high salinity, which jellies thrive in." The Australian natives have now spread along the continental shelf, extending across the Mississippi Sound and along the Louisiana and Texas coasts to the west side of the Mississippi River. The short-term question is will they survive the winter? The long-term question is what can be done about them? There are no easy answers.
Spotted jellies don't have much of a sting and thus are not considered dangerous to humans, but the ecological implications of such a widespread invasion are extremely worrisome. "Jellies put off a lot of mucous, and the water in the areas of densest concentrations is extremely viscous," says Graham. "Copepods Ñ very small grazers Ñ in the areas we surveyed were very lethargic and not producing eggs. In addition, zooplankton numbers appeared to be substantially reduced." Zooplankton is the animal component of plankton, small crustaceans and fish larvae that float or drift in great numbers at or near the surface, and serve as a basic component of the food chain for fish and other larger organisms. Gulf fishermen are upset; the jellies are voracious predators in an area known as the Fertile Fisheries Crescent. The brown shrimp fishery that is coming to an end has already been impacted. Large concentrations of the jellies present a physical barrier to shrimpers, says Perry. "They clog the nets and can tear the webbing out of trawls. The fishermen want to know what we're going to do about it." The white shrimp fishery opens in early fall. "The jellies are really efficient filter feeders," says Perry. Graham described one area with a large concentration of spotted jellies as "a big hole in the water," devoid of food and other prey. Information gathered on the Pelican will help determine whether the jellies are eating the larvae of shrimp, crabs, oysters, and other fish, or feeding on the food that helps other species survive, or both. The problem is not confined to the Gulf of Mexico; jellyfish blooms and invasions have been increasing worldwide