“Most comb jellies have little direct effect on humans, except through a minor role in marine food webs. One species, however, stands apart as the villain of the basal invertebrates. In the 1980s, the Atlantic comb jelly Mnemiopsis was accidentally introduced into the Black Sea, probably in ballast water carried by commercial shipping. Once in its new environment, away from natural competitors and predators, it reproduced rapidly – all the while consuming vast quantities of larval fish and crustaceans. Some (controversial) estimates placed the total seething mass of diminutive comb jellies in the Black Sea at over half a billion tonnes. The local anchovy fishery, already under heavy fishing pressure, was decimated. While ecologists debated what to do, a possible solution arrived, unplanned, in the shape of another accidental introduction. The newcomer was a second comb jelly, this time the voracious Beroe. Fortuitously, Beroe does not eat fish or crustaceans, but is instead a specialist predator of other comb jellies and nothing else. As the invading Beroe now feast on the Mnemiopsis, the fish stocks are showing gradual and welcome signs of recovery.” Invasive Species Book:The Animal Kingdom: A Very Short Introduction Source: The Animal Kingdom: A Very Short Introduction