eDNA-based crayfish plague detection as practical tool for biomonitoring and risk assessment of A. astaci -positive crayfish populations

While environmental DNA (eDNA) approaches have the potential to revolutionize biodiversity research and monitoring, most aquatic biomonitoring and management programs still rely on conventional monitoring methodologies. Here we evaluated the suitability and robustness of an eDNA-based approach for the detection of the crayfish plague agent Aphanomyces astaci and assessed the capacity of this new method as practical tool for bioassessments in freshwater. The approach was examined in three case studies: case study A tested its use as biomonitoring tool to determine the range and density of A. astaci - infected crayfish populations in three different water systems. Case study B focussed on the identification of possible A. astaci infection sources, here an aquafarm. For case study C we assessed a migration front of infected crayfish near a native crayfish area. The eDNA-based detection allowed to infer local patterns and distribution limits of crayfish plague occurrence. Spore estimates in eDNA samples correlated significantly with catch per unit effort values and pathogen loads of captured A. astaci - positive crayfish obtained from trapping in running waters. We also showed that spore concentrations are detectable up to three kilometres downstream from hot spot areas of infected crayfish. By identifying a possible A. astaci entry point and migration front eDNA proved suitable for the detection of A. astaci spores at low population densities and/or pathogen levels of infected crayfish. The study provides conclusive evidence for the suitability of the eDNA approach as a tool for risk assessment and large-scale monitoring of A. astaci for a wide range of practical conservation issues of indigenous crayfish species.