Columbia River Signal Crayfish

<em>Pacifastacus leniusculus</em>, the Columbia River signal crayfish, is a freshwater crustacean in the family Astacidae native to the Pacific Northwest of North America and widely introduced across Europe, Japan, and other regions. This species has not been evaluated by the IUCN but is recognised as one of the most ecologically damaging invasive freshwater species in Europe, present in 26 European countries, Japan, and its native range in the United States. Signal crayfish are large, aggressive, and highly fecund, capable of displacing native crayfish species through competition and through transmission of crayfish plague, a disease caused by the oomycete <em>Aphanomyces astaci</em>, to which North American crayfish have evolved resistance but European species have not. This species inhabits a wide range of freshwater environments including rivers, streams, lakes, and estuaries, as well as adjacent terrestrial habitats. Signal crayfish are omnivores, consuming aquatic plants, invertebrates, fish eggs, and organic detritus, and their burrowing activity can destabilise stream banks and increase turbidity. Management of invasive populations is a major focus of freshwater conservation in Europe. Biological traits of this species remain poorly documented in the scientific literature.