The white-clawed crayfish, Austropotamobius pallipes, is a unique freshwater invertebrate native to Europe, including the British Isles. It represents the sole indigenous crayfish species in the United Kingdom and Ireland. This crustacean plays a role in aquatic ecosystems, contributing to the health of the waterways it inhabits. Its presence can indicate a balanced and healthy freshwater environment, making it a subject of considerable interest for environmental conservation efforts.
Identifying Features
The white-clawed crayfish has an olive-brown body with a textured, pitted appearance on its carapace. Adults reach a length of up to 12 cm. A distinguishing characteristic is the pale underside of its claws, which gives the species its common name.
The body is divided into two main sections: the head and thorax, separated by a cervical groove. Behind this groove, on the carapace, there is a row of sharp spines or small tubercles. A single, narrow post-orbital ridge is located just behind each eye. The top surfaces of the claws feel slightly granular to the touch.
Natural Habitat and Ecological Role
White-clawed crayfish prefer clean, well-oxygenated freshwater environments such as rivers, streams, canals, and lakes. They are found in areas with stony or rocky substrates, where they seek refuge under submerged rocks, logs, or in crevices. They also utilize tree roots, fallen leaves, and aquatic vegetation for shelter and foraging. These crustaceans can tolerate a range of water depths, from shallow streams to deeper, slow-flowing rivers up to 2.5 meters.
As omnivores, white-clawed crayfish consume a varied diet including dead organic matter, algae, aquatic invertebrates, water plants, and even other crayfish. This scavenging behavior helps to keep waterways clean by breaking down detritus and cycling nutrients, influencing the composition of species in their community. Their presence signals good water quality, making them a bioindicator species for the health of freshwater ecosystems. They are also a food source for other aquatic animals, including otters, herons, and large fish like eels and carp.
Threats and Protection Efforts
The white-clawed crayfish faces numerous threats, leading to a significant decline in its populations across Europe, with a 70% decrease in numbers since the 1970s. The most severe threat comes from the invasive North American signal crayfish, Pacifastacus leniusculus. Signal crayfish are larger, reproduce more quickly, and aggressively outcompete the native species for food and shelter.
A major consequence of the signal crayfish’s introduction is the spread of crayfish plague, caused by the fungus Aphanomyces astaci. While signal crayfish are carriers and immune to this disease, it is highly lethal to white-clawed crayfish, wiping out entire populations within weeks. Other threats include habitat degradation, pollution from agricultural runoff and industrial discharge, and the effects of climate change.
Conservation efforts are underway to protect this species. The white-clawed crayfish is legally protected under European directives and national legislation. These protections prohibit taking or disturbing the species from the wild and mandate the designation of Special Areas of Conservation (SACs) for its protection.
Captive breeding programs aim to produce healthy populations for release into carefully selected “ark sites”—isolated refuge habitats free from invasive species and disease. Habitat restoration also supports existing populations. Measures to control signal crayfish populations and prevent their spread are being implemented to mitigate the impact of this invasive threat.