Use of Environmental DNA for Early Detection of Invasive Elodea Species in Interior Alaska

Invasive Canadian waterweed Elodea canadensis and western waterweed E. nuttallii are a threat to native salmon Onchorhynchus spp. in Alaska. Early detection is important to stop or mitigate spread. We evaluated detection of environmental DNA (eDNA) as a tool for early detection of these invasive species in Alaska. First, we evaluated four quantitative real-time PCR assays, one for each species, and two targeting either species, using samples taken at known infestations in Chena Lakes and Potter Marsh, Alaska. We also deployed E. nuttallii in screened containers at the Small Arms Complex Pond, Fort Wainwright, Alaska (Test Pond), in 2018 and 2019 to evaluate the detection of eDNA as a function of distance from the containers. At the known infestations, we detected the eDNA of both species in water samples. However, in our Test Pond, we only detected Elodea eDNA in 2 of 126 samples collected in 2019. Both detections were from samples collected within 10 cm of the containers. There were no detections in 60 samples collected in 2018 at the Test Pond. While there are potential uses for the eDNA markers we developed (e.g., species identification), we found no evidence to support their use as an early-detection tool for Elodea in Alaska.