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Jellyfish Gone Wild — Text-only | Flash Special Report
Black Sea


If the world had an official jellyfish capital, it would surely be the Black Sea--a huge inland sea located between Europe and Asia. Why? Because the Black Sea was transformed into a veritable jellytorium during the 1990s by an invasion of Mnemiopsis, a voracious, rapidly-reproducing species of comb jelly.

At its most jellified state during the late 1990s, the Black Sea harbored more than one billion tons of Mnemiopsis--which equals more than 10 times the weight of all fish caught throughout the worl----d annually. In some parts of the Black Sea, each cubic meter of water-- a space comparable to the interior of a large garbage bag--teemed with thousands of the golf ball-sized jellies.

The domination of Mnemiopsis over the Black Sea started in 1982--probably when a U.S. ship jettisoned into this sea ballast water from the U.S., along with some hitchhiking Mnemiopsis. This comb jelly is a hardy ecological squatter that is rapidly spreading along the east coast of the U.S. but had previously never visited the Black Sea.

Nevertheless, the Black Sea, Europe's most polluted ocean, provided a particularly hospitable environment to the Mnemiopsis newcomer. Why? Because the Black Sea has no natural predators of Mnemiopsis and because its overfished waters offered Mnemiopsis only minimal competition from fish. Feasting on copious quantities of plankton and able to shed 8,000 eggs daily, Mnemiopsis reproduced with wild abandon.

Swarming from coast to coast, Mnemiopsis crowded out almost all fish in the Black Sea. The result: losses of hundreds of millions of dollars to the area's fishing and tourism industries.

The tide only turned on Mnemiopsis in 1997, when another invading species of comb jelly, called Beroe, arrived in the Black Sea, probably also via ballast water from the U.S. Because Beroe eats Mnemiopsis, it has helped tame the Black Sea's Mnemiopsis monster.

Moreover, because Beroe eats nothing but Mnemiopsis and disappears as Mnemiopsis disappears, it has improved its adopted habitat without causing ecological problems--a rarity for an introduced species.

Nevertheless, Mnemiopsis remains a serious problem. Why? Because even though Mnemiopsis is controlled in the Black Sea through Beroe-assisted jellycide, it still greatly impacts area ecology. Additionally, Mnemiopsis has fanned out from the Black Sea via canals and ships to the Caspian, Azov and Mediterranean Seas. Also, additional waves of U.S.-based Mnemiopsis have recently invaded the North Sea and the Baltic Sea.

Just as it did in the Black Sea, Mnemiopsis has significantly reduced fish catches in many of these other huge seas. Indeed, Mnemiopsis has caused even more damage to fisheries in the Caspian Sea than it did in the Black Sea.

Some European nations have considered intentionally introducing Beroe into their Mnemiopsis-infested waters. But so far, they have refrained from doing so for fear of unintended ecological consequences from such introductions. Moreover, it is uncertain whether Mnemiopsis-infested waters besides the Black Sea meet Beroe’s requirements for salinity, temperature and other environmental conditions.



The march of the invasive comb jelly (Mnemiopsis), which originated in the U.S.
Credit: Tamara Shiganova

The fishing and tourism industries suffered more than $350 million in losses from the explosion of the comb jelly in the Black Sea. Losses from an ongoing comb jelly explosion in the Caspian Sea are expected to exceed Black Sea losses. Two comb jellies are shown here. Credit: Jan-Erik Bruun, Finnish Institute of Marine Research