Testing the Role of Stream Flow on eDNA Abundance Using the Invasive Asian Clam Corbicula Spp

The efficacy of environmental DNA to assay the presence of invasive species hinges upon understanding the covariates influencing fate and transport. In lotic systems, these covariates may include biotic (e.g. invasive species density, seasonal activity patterns, etc.) and abiotic (e.g. stream discharge, temperature, ultraviolet irradiation, pH, etc.) factors, as well as their complex interactions. To better understand fate and transport of eDNA in complex lotic systems, we assessed eDNA copy number for invasive Asian clams (Corbicula spp.) in paired freshwater streams in central Illinois via a primer/probe assay. We collected eDNA samples approximately every two weeks for one year, as well as during periods of high and low discharge. At each sampling period, we collected data for a number of water quality variables (including pH, temperature, turbidity, conductivity, total dissolved solids, and salinity), and we also conducted mid-summer quadrat sampling at each site to estimate Corbicula densities. Importantly, we placed our two sampling sites at USGS stream gages in order to access continuous discharge data. We anticipated that high stream flow events could either dilute eDNA concentrations or increase eDNA concentrations by mobilizing Corbicula DNA from the sediments. We found abundance of Corbicula eDNA as copy number increased with increasing water temperatures, likely reflecting a late spring and early summer reproductive peak for this species. However, we found a weak and non-significant negative relationship between stream flow and Corbicula eDNA abundance, despite having sampled at base flow and high flow conditions across multiple seasons. As such, we conclude that stream discharge may have little effect on estimates of eDNA abundance for common stream and river species like the invasive Asian clam, although more studies should seek to evaluate the role of stream and river flow regimes on eDNA performance.