Moscow , Shirshov Institute of Oceanology, Russian Academy of Sciences
Ctenophora beroe, invertebrate jelly-fish of prey, has appeared in the Black Sea. Scientists expect that the new inhabitant will help to restore the damaged ecosystem of the Black Sea.
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Researchers from the Institute of Oceanology and its South Department in Gelendgik have observed Ctenophora beroe in the north-eastern part of the Black Sea. This predatory jelly-fish made its appearance in the Black Sea in 1997. Now it feels itself at home eating up the other kind of Ctenophora - mnemiopsis. C. mnemiopsis has caused serious damage to the Black Sea ecosystem, so the researchers believe the appearance of C. beroe is for the better. They hope that C. beroe will help to restore the Black Sea ecosystem.

Mnemiopsis was brought into the Black Sea with ballast waters in the 1980s. Its appearance became a cause of the environmental trouble. The mnemiopsis population expanded so intensively that its total biomass increased up to one milliard tons. In 1990-1992 the situation became critical. Mnemiopsis feeds mainly on animal plankton. As a result populations of other fish fed on plankton, such as Black Sea anchovy, scad and sprat, sharply decreased. Some kinds of fish suffered because mnemiopsis ate their larvae.

The situation was so serious that experts from international commission GEZAMP proposed to bring into the Black Sea some predator able to eat mnemiopsis. One of candidates was the other kind of Ctenophora, C. beroe. But at that time the scientists didn't dare to do it being unsure of the result. To their surprise, in 1997, C. beroe appeared in the Black Sea themselves without any invitation. Evidently, it came from the Marble Sea. At first time they settled down in a few coastal parts of the Black Sea, but in 1999 they already occupied the whole north-east region of the Black Sea. This gave the scientists possibility to watch C. beroe.

First of all the scientists wondered what C. beroe feed on. By the way any Ctenophora, including beroe and mnemiopsis, look like big soap-bubble, sometimes oval, sometimes flattened, with two long tentacles near oral hole and meridional lines of cilia on the surface of the bubble. Ctenophora beroe's body is transparent and jelly-like. (Ctenophora is commonly named "jelly-fish", like medusa). So it's easy to watch jelly-fish's digestion. It turned out that C. beroe cannot digest plankton, medusa and young fish. They feed on animals similar to themselves, that is mnemiopsis. Beroe sucks mnemiopsis into oral hole and its body swells. It takes 3-5 hours to digest a prey.

According to estimate, beroe can eat up from 4 to 30% of mnemiopsis population a day. It looks like truth because population of mnemiopsis has decreased considerably and at the same time population of beroe has increased. Besides, C. beroe have become larger - up to 16 cm in diameter.

It is not clear yet would beroe be permanent inhabitants of the Black Sea. Probably low temperature and low salt concentration in water will not allow beroe to spend winter in the Black Sea. The scientists think that beroe will come and settle in the Black Sea only from August till November that is optimum season, when beroe feel very comfortable in the Black Sea. The scientists hope that C. beroe will restore the balance of the Black Sea ecosystem.


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