Leidy's comb jelly was introduced to the Black Sea in the early 1980s from the United States. The absence of competitors and predators allowed this ctenophore to flourish with a total biomass of about 1,000,000,000 tons. As a result of the huge amount of food consumed by the exploding comb jelly population, many fish fry starved. Along with over-fishing and pollution, the introduction of Leidy's comb jelly has been cited as an important factor in the collapse of commercial fisheries in the Black Sea in the 1990's.
