Year-round monitoring and large-scale screening of native and invasive crayfishes in lotic systems

Freshwater crayfish are among the most threatened animal taxa in Central Europe. Effective conservation measures for endangered native and management of invasive alien crayfishes requires knowledge about distribution, monitoring existing early detection newly established populations. eDNA has recently emerged as a promsing, highly sensitive, non-invasive tool this regard. To evaluate freshwater crayfish, we developed novel set specific eDNA-assays all ( Austropotamobius torrentium, pallipes, Astacus astacus ) relevant species Pacifastacus leniusculus, Faxonius limosus, immunis ensure specificity each primer pair was tested silico , vitro, situ, including total 13 lotic lentic waterbodies (Fig. 1). Moreover, assessed influence spatio-temporal variables (distance to upstream population, season, stream size) on seven streams using two different methods (qualitative endpoint PCR quantitative droplet digital PCR, ddPCR). The assays successfully detected across habitats. Multiple linear mixed-effects analysis revealed significant effect distance season rate (endpoint PCR) eDNA-concentration (ddPCR). Year-round successful up 7 km downstream source although detectability lowest winter. further decreased with increasing size. Finally, correlated positively estimated population Overall, our study provides easily applicable 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 accounted for. We therefore recommend implementing eDNA-detection complementary survey tool, particularly large-scale screening data-deficient catchments (Chucholl et al. 2021).