Crayfish Plague in Europe

Abstract

The crayfish plague is caused by fungal-like water molds that exclusively live in the shells of freshwater crayfish. In its native North America, it is a fairly benign parasite, as the crayfish species living there have mechanisms to slow down the hyphae penetration of the shell. Crayfish species on other continents lack those protective mechanisms and succumb. The plague came to Italy around 1860. During the following 100 years, the crayfish plague spread over Continental Europe and Scandinavia, and all but exterminated the European crayfish species where it came. To compensate for the loss of the crayfish fishery, when hundreds of re-implantation attempts had failed and no tolerance to the plague seemed to develop, the signal crayfish was brought from the USA to Sweden and subsequently to most other European countries. There the signal crayfish turned into a major vehicle for the further spread of the plague. This way the crayfish plague got to Britain.

Now the signal crayfish itself is seen as a problematic invader, and it is on an EU list of 37 invasive species that should be exterminated if at all possible, despite the fact that economically it has more or less done what it was imported to do.