PS 22-46 - Detection and conservation of endangered Spectaclecase mussels in the Upper Mississippi River

Abstract: Spectaclecase (Cumberlandia monodonta) are endangered freshwater mussels native to large rivers in the Mississippi River drainages of the midwestern and southeastern United States. To aid in conservation of Spectaclecase populations, agencies including the US Army Corps of Engineers, Minnesota Department of Natural Resources, and Wisconsin Department of Natural Resources are conducting habitat restoration efforts along the Upper Mississippi River (UMR). Few extant populations of Spectaclecase are known in the UMR and additional occurrence data would better inform restoration efforts. Spectaclecase are typically surveyed using traditional dive methods, but their habit of occupying sheltered areas, like large interstitial spaces or crevices, makes diving dangerous, expensive, and time-consuming. Environmental DNA (eDNA) can be an efficient alternative for monitoring aquatic taxa; however, freshwater mussels often have low detection rates. Previously, a quantitative PCR (qPCR) assay was developed for Spectaclecase that detected existing populations. Here, our objective was to extend the previous work by conducting eDNA surveys across the UMR to evaluate detection and identify new populations. From 2020-2022, we collected eDNA samples at 200 sites across 17 pools within the UMR. At each sampling site, we collected four 50-ml benthic samples. Water samples were centrifuged, DNA extracted, and assessed using the existing Spectaclecase eDNA marker. We conducted dive surveys at any new locations identified by eDNA to attempt to confirm presence. We demonstrated that eDNA can detect previously unknown populations of Spectaclecase, although some known sites were not detected through eDNA. Dive surveys demonstrated that a positive, but weak, eDNA detection was enough to discover Spectaclecase mussels. Our work demonstrates that eDNA can be an effective tool for monitoring this endangered species, while also illustrating some of the challenges of detecting declining mussels in large river systems.