Jellyfish invasion

Comb jellyfish, the world's most dangerous alien species, is invading the Caspian Sea after having run wild on the Black Sea. It's killed anchovies, decimitated the kilka population and is threatening caviar:

A self-fertilising hermaphrodite, Mnemiopsis breeds as fast as it eats. It reaches maturity within two weeks and then produces 8,000 eggs daily. Its appetite is so great that it can double its size in a day. By 1990, its total biomass in the Black Sea had reached an estimate 900 million tonnes, 10 times the annual fish catch from all the world's oceans.
One snorkelling marine biologist from the Ukraine, Yu Zaitsev, calculated that there were 500 of the beasts in a single cubic metre of water in Odessa Bay. There was almost more jellyfish than water. Meanwhile, fish catches across the Black Sea had declined by 90 per cent. The valuable anchovy virtually disappeared.