context: On the other hand, in the late 1980s the Western Atlantic ctenophore Mnemiopsis leidyi was accidentally introduced into the Black Sea and Sea of Azov via the ballast tanks of ships, and has been blamed for causing sharp drops in fish catches by eating both fish larvae and small crustaceans that would otherwise feed the adult fish. Mnemiopsis is well equipped to invade new territories (although this was not predicted until after it so successfully colonized the Black Sea), as it can breed very rapidly and tolerate a wide range of water temperatures and salinities. The impact was increased by chronic overfishing, and by eutrophication that gave the entire ecosystem a short-term boost, causing the Mnemiopsis population to increase even faster than normal – and above all by the absence of efficient predators on these introduced ctenophores. Mnemiopsis populations in those areas were eventually brought under control by the accidental introduction of the Mnemiopsis-eating North American ctenophore Beroe ovata, and by a cooling of the local climate from 1991 to 1993, which significantly slowed the animal's metabolism. However the abundance of plankton in the area seems unlikely to be restored to pre-Mnemiopsis levels.
question: How was the population of mnemiopsis in The black Sea and the Sea of Azov brought under control?
answers: by the accidental introduction of the Mnemiopsis-eating North American ctenophore Beroe ovata, the accidental introduction of the Mnemiopsis-eating North American ctenophore Beroe ovata the accidental introduction of the Mnemiopsis-eating North American ctenophore Beroe ovata, and by a cooling of the local climate from 1991 to 1993