Comb jellies (Mnemiopsis ledyi) have increased again in Finnish water. Just a month ago it appeared that the invasive plankton was decreasing in Finnish waters, and that it might disappear completely.
Now the research vessel Aranda of the Finnish Institute of Marine Research found them in large numbers in both the Gulf of Finland and the Åland Sea. Numbers were as high as in the worst time in the winter.
Although it is very small, the comb jelly consumes young fish as well as edible zooplankton, making it a serious potential hazard for fish stocks.
Native to the east coast of North America, the comb jelly has spread around the world, mainly in ballast water carried in ships.
It has already caused serious damage to fish stocks in the Black Sea.
