eDNA Detection of Native and Invasive Crayfish Species Allows for Year-Round Monitoring and Large-Scale Screening of Lotic Systems

Effective management of both endangered native and invasive alien crayfishes requires knowledge about distribution, monitoring existing early detection newly established populations. Complementary to traditional survey methods, eDNA sampling has recently emerged as a highly sensitive non-invasive method monitor crayfish To advance the use tool for we used twofold approach: 1) designed novel set specific eDNA-assays all ( Austropotamobius torrentium, pallipes, Astacus astacus ) most relevant species Pacifastacus leniusculus, Faxonius limosus, immunis in Central Europe. ensure specificity each primer pair was tested silico , vitro, situ ; 2) assessed influence spatio-temporal variables (distance upstream population, season, stream size) on seven streams using two different methods (qualitative endpoint PCR quantitative droplet digital PCR, ddPCR). The developed assays successfully detected across lotic lentic habitats. rate (endpoint PCR) eDNA-concentration (ddPCR) were significantly influenced by distance season. successful up 7 km downstream source population seasons, although detectability lowest winter. further decreased with increasing size. Finally, correlated positively estimated Overall, provide near operational six species, enabling year-round detection, which represents clear benefit over conventional methods. Due its high sensitivity, is also suitable targeted search as-yet unrecorded or emerging Using ddPCR might allow rough estimation size, provided that identified factors are accounted for. We therefore recommend implementing eDNA-detection complementary tool, particularly large-scale screening data-deficient catchments monitoring.