Invasive Species Monitoring Is Improved by Combining eDNA qPCR and Traditional Microscopy Methods

ABSTRACT Preventing the spread of aquatic invasive species, such as non‐native molluscs, plants, and fish, hinges on early detection to help managers avoid establishment. Here, we evaluated two detection methods for a prolific invader: dreissenid mussels. We compared environmental DNA (eDNA) testing to cross‐polarized light microscopy detection (CPLM) of dreissenid larvae (veligers). Microscopy is widely used for dreissenid detection, whereas eDNA testing is not yet common. We analysed 85 samples collected from July 2014 to September 2015 from two water bodies in Minnesota with known infestations of zebra mussels ( Dreissena polymorpha ), and one water body (Duluth/Superior Harbour in Lake Superior) that is infested with both zebra and quagga mussels ( Dreissena rostriformis ). Using a probe‐based quantitative PCR eDNA assay, we detected Dreissena eDNA in 34 of the 62 veliger‐negative samples and 11 of the veliger‐positive samples, whereas eDNA was not detected in 12 of the veliger positive samples. Our results suggest managers and researchers could improve early detection sensitivity by using eDNA testing of plankton tow‐net sampling to complement microscopy detection of invasive bivalves. eDNA technologies, including large‐volume tow‐net sampling (with or without veligers present in the waterbody), can help prevent false negative detection outcomes and improve early detection of invasive mussel species.