Impacts of the North American signal crayfish (Pacifastacus leniusculus) on European ecosystems

As a vector of the crayfish plague (Aphanomyces astaci), invasive crayfish pose a major threat to endemic crayfish species in Europe. But do they affect whole ecosystems and fish species as well? A comprehensive review was done using online search engines on current literature to elucidate possible crayfish effects. It showed that they have the potential to decimate benthic invertebrate populations as well as submerged plants—the first a necessary food source, the second an important part of the habitat of fish, functioning as hiding space for their fry as well as their prey. Crayfish are suspected to act as bioturbators as well, by influencing preconditions to certain algae and animals while sorting through the substrate of a river. Their long-term effects on fish so far are inconclusive. Studies on this matter showed no effect, selective impact on fish that share prey with the crayfish, as well as significantly negative effects on fish in general. In shorter examinations, invasive crayfish have proven to displace fish from shelters, putting them at a higher risk for predation. Moreover, comparisons to native crayfish species showed that these had less negative effects on fish—due to lower consumption and reproduction rates and population densities.