Environmental DNA detection of the invasive mussel Mytella strigata as a surveillance tool

The American charru mussel Mytella strigata (Hanley, 1843) is an invasive species of great concern along the shores of North America and Asia. As with most invasive mussels, it is very difficult to eradicate once established. Surveillance therefore plays a vital role in controlling its spread. Molecular tools like environmental DNA (eDNA) have proved to be useful in recent years to assist in the early detection and management of invasive species, with considerable advantages over conventional methods like substrate monitoring and sampling, which can be relatively laborious and time-intensive. This technique can be particularly useful in the initial stages of invasion when the population density is often too low to be detected by visual surveys alone. In the present study, we developed a species-specific quantitative polymerase chain reaction (qPCR) approach targeting a cytochrome c oxidase subunit I (COI) DNA fragment aimed at detecting the presence of M. strigata from water samples. We also investigated the relationship between mussel cover and eDNA concentration. Our approach was tested on coastal seawater samples from 14 sites in Singapore, supported by conventional visual quadrat surveys. The results showed clear, positive M. strigata eDNA detection for all sites where this species was observed visually during field surveys. However, there was a weakly negative correlation between percent mussel cover and eDNA concentration, indicating that mussel abundance could not be estimated reliably using seawater eDNA alone. Nevertheless, this study underscores the effectiveness of eDNA in informing the presence and distribution of M. strigata along extensive coastlines comprising different habitats. This approach contributes to a robust toolkit for routine surveillance at sites where invasion may be impending to control the spread of the invasive mussel.