Evaluation of blue mussel (Mytilus edulis) as a natural sampler of environmental DNA and pathogens in aquaculture

In recent years analysis of environmental DNA has shown promising results for biodiversity monitoring. The area of applicability for eDNA-based methods is extending and has been proposed as an approach to detect and monitor pathogens in aquaculture. Filter feeding organisms have been advocated as ideal candidates as natural samplers of eDNA due to their ability to efficiently filter water. Several studies have been performed to evaluate the potential of natural samplers, but mainly their ability to detect eDNA from fish species in comparison to visual or traditional surveys. In this study, eDNA from blue mussel samples and water samples collected near an aquaculture site for 15 months were amplified and sequenced with the Leray XT primer set for COI to compare the eDNA diversity obtained from the two sampling methods and their ability to detect pathogens and harmful species. In the blue mussel samples, 718 species were detected which was lower than half the number of species detected in the water samples (2250), and a significant difference in the eDNA community retrieved with the two sampling methods was observed. Seasonal signals between samples collected in the “summer months” (May-October) and “winter months” (November-April) were detected in both blue mussel samples and water samples, but the three main species that contributed most to these signals were different for the two sampling methods. The water samples had a higher species richness and abundance in all pathogens detected except for one species, Paramoeba sp. Even though the species richness and abundance were greater in the water samples than in the blue mussel samples, the blue mussels have shown the ability to detect eDNA in seawater and that they can be used as natural samplers. The blue mussels present an opportunity to easily avoid the processing and filtration that aquatic eDNA samples require, but further investigation of which species the blue mussels are able to detect will provide information on where the use of blue mussels as natural samplers could be most suitable