Invasive species pose a major threat to global biodiversity. In the UK, one of the most notorious of these invaders is the signal crayfish, Pacifastacus leniusculus. Introduced from the US in the 1970s to be reared in farms for restaurants and food shops, this species quickly became established in the wild. Accidental and intentional releases helped them spread throughout British rivers and streams and today, they’re prevalent across the UK and continental Europe.
Signal crayfish have been so successful at invading because they produce a lot of offspring and eat almost anything, from detritus and aquatic plants to small invertebrates, fish and even each other.
Their extensive burrowing has eroded river banks throughout the UK, and they pose a grave threat to native wildlife, including Britain’s only native crayfish species, the white-clawed crayfish Austropotamobius pallipes. Signal crayfish carry a disease known as crayfish plague, which is 100% lethal to the native white-clawed if contracted. But even signal crayfish free of the disease tend to outcompete their native counterparts over time. Pollution also threatens white-clawed crayfish across much of their range, and as a result, they have suffered tremendous declines, estimated at over 90% in some English counties, leaving them vulnerable to extinction. MORE
Header image: Also known as the European freshwater crayfish, the white-clawed crayfish is endangered. Credit: Eleri Pritchard, Author provided.