Active and passive environmental DNA surveillance of aquatic invasive species

Environmental DNA (eDNA) is useful for delimiting species ranges in aquatic systems, whereby water samples are screened for the presence of DNA from a single species. However, DNA from many species is collected in every sample, and high-throughput sequencing approaches allow for more passive surveillance where a community of species is identified. In this study, we use active (targeted) and passive molecular surveillance approaches to detect species in the Muskingum River Watershed in Ohio, USA. The presence of bighead carp (Hypophthalmichthys nobilis) eDNA in the Muskingum River Watershed was confirmed with active surveillance using digital droplet polymerase chain reaction (ddPCR). The passive surveillance method detected the presence of eDNA from northern snakehead (Channa argus), which was further confirmed with active ddPCR. Whereas active surveillance may be more sensitive to detecting rare DNA, passive surveillance has the capability of detecting unexpected invasive species. Deploying both active and passive surveillance approaches with the same eDNA samples is beneficial for invasive species management.