Bay comb jellies studied as cure for the Black Sea

February 02, 1993|By Douglas Birch | Douglas Birch,Staff Writer

CABRIDGE — CAMBRIDGE -- A Russian scientist searching for a way to combat a recently imported animal that has devastated commercial fishing in the Black Sea region thinks the answer may lie in a predator found lurking in the Chesapeake Bay.

It isn't very fierce looking, as predators go. It lacks jaws, ranges in size from a thumbtack to a small cup, paddles around below the surface of the water and glows in the dark.

But Beroe grazilis, one of a number of gelatinous blob-like animals called ctenophores (teen-oh-fores) by scientists and "comb jellies" or "glowballs" by fishermen, has a healthy appetite. And Dr. Stanislav P. Volovik of the Research Institute of Azov Sea Fishery Problems, who visited the University of Maryland's Horn Point research center on Wednesday, thinks Beroe could be the answer to a huge problem.

In 1982, another type of ctenophore called Mnemiopsis leidyi first appeared in the Black Sea, in the waters off Constanta in Romania. Dr. Volovik said they are native to the Atlantic coast of North and South America, and may have been carried through the Bosporus in the ballast water of ships visiting from Cuba, the United States or Brazil.

In the Black Sea, Mnemiopsis found itself free of natural predators, such as its cousin the Beroe and various Atlantic jellyfish species, including the Chesapeake Bay's sea nettles.

It flourished, gobbling up the zooplankton that is the staple diet of many commercial fish. It also ate their eggs and larvae.

While they resemble jellyfish, comb jellies are not closely related to them, said Jennifer Purcell, associate professor at the University of Maryland's Center for Environmental and Estuarine Studies.

Within three years, Dr. Volovik said, the annual catch of anchovies, herring and other important commercial fish in the Black Sea plummeted from about 800,000 tons to 50,000 tons.

Mnemiopsis slipped through the Kerch Strait and was first spotted in the Azov Sea in 1988. In a single

year, the catch of sprat dropped from 120,000 tons to about 25,000 tons, Dr. Volovik said. The anchovies were nearly wiped out.

The shallow Azov, with a maximum depth of just 46 feet, is heavily polluted with oil, heavy metals, nutrients and pesticides. But none of these pollutants has had the impact of Mnemiopsis, which between April and November can choke the Azov with up to 300 creatures per square foot.

Last May, representatives from the Black Sea states of Russia, Georgia, Ukraine, Turkey, Bulgaria and Romania met to figure out how to tackle the Mnemiopsis problem.

One outgrowth of that meeting is Dr. Volovik's study, sponsored in part by the United Nations Development Program.

Dr. Volovik is working with Richard Harbison, an American scientist with the Woods Hole Oceanographic Institution in Massachusetts. Both scientists have concluded that the only way to combat the Mnemiopsis is by importing a predator, Dr. Volovik said.

But Dr. Harbison favors introducing a foreign commercial fish species that also eats Mnemiopsis to the Black and Azov seas. (There are about 350 species of fish that feed on comb jellyfish, including butterfish, cod and varieties of herring.)

Dr. Volovik thinks a new fish species might take many years to establish itself, while ctenophores have demonstrated their ability to thrive in the affected waters. And something should be done quickly, he said.

The people of the region, though, will have to wait for at least a year pending the results of further research, he said.

"The main questions are: Can any organism be a good predator to Mnemiopsis in our region? And can this organism destroy our ecosystem in the same way as Mnemiopsis?" he said.

To make sure his proposed cure, Beroe, isn't worse than the disease, Dr. Volovik said he needs a better "understanding of the place of the organism Beroe, in the ecosystem" -- its eating habits, reproduction, and tolerance for salinity levels and temperatures.

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