Native and invasive freshwater decapods in the UK: conservation and impacts

Crayfish species have been translocated by humans, with both positive and negative consequences. Conservation-led translocations of the endangered white-clawed crayfish (Austropotamobius pallipes) to safe ‘Ark sites’ where threats are minimised are underway. Restored quarries may represent ideal Ark sites and several questions pertaining to their suitability were addressed, along with a 3-year case study of Ark site creation in a limestone quarry. Quarries contain large quantities of unconsolidated sediment and crayfish experienced gill fouling and reduced aerobic scope after exposure to suspended solids concentrations of 62 mg L-1 and above. A novel parasite detected in the gills of A. pallipes caused gill pathology, highlighting the need for health assessment of donor stock prior to translocation. Most Ark sites do not historically hold crayfish and their introduction may cause strong effects on existing freshwater communities. In a mesocosm study, juvenile and adult A. pallipes reduced the abundances of grazers and shredders; however consumption of the gastropod Physa fontinalis and detritus varied between life-stages. The American signal crayfish (Pacifastacus leniusculus) is rapidly invading catchments and replacing A. pallipes. In a field-based telemetry study, a flow-gauging weir reduced upstream movements of P. leniusculus by 45%, highlighting the need to balance invasion risk with EU targets for improved riverine connectivity. P. leniusculus co-occurs with another invasive decapod, the Chinese mitten crab (Eriocheir sinensis), and their feeding behaviour was compared. Both consumed a range of prey items, including fish eggs. Juvenile E. sinensis had a higher per capita intake of the keystone shredder Gammarus pulex than native A. pallipes and showed greater preference for this prey item than did P. leniusculus. Overall, E. sinensis is likely to have an equal, if not higher, per capita impact on prey species than P. leniusculus. Recommendations for quarry Ark site creation and management of invasive decapods were formulated.