Seasonal patterns of environmental DNA detection for freshwater unionid mussels

Environmental DNA (eDNA) provides a powerful non-invasive tool for monitoring freshwater mussel assemblages, yet detection probabilities can be influenced by reproductive behaviors, seasonal vertical migration, and hydrological conditions. This study assessed eDNA detection from April through October across two diverse mussel beds in Ohio, encompassing species with both tachytictic (short-term brooders) and bradytictic (long-term brooders) reproductive strategies. Mussel DNA was consistently detected across seasons, with detection patterns generally aligning with species observed through a visual tactile survey. Overall, the eDNA sequence abundance was positively correlated with tactile mussel counts, however congruence between the two surveys was strongest during low discharge and when the surveys occurred in close temporal proximity to one another. This study finds that eDNA sampling for freshwater mussels performs adequately within the currently prescribed survey window for visual surveys. However, seasonal factors such as endobenthic burial behavior and high discharge events may have reduced detection efficiency, particularly in Killbuck Creek, where species richness was lowest during periods of high flow in early spring. Therefore, decisions made regarding the timing of eDNA surveys should consider local environmental conditions (e.g., temperature and flow) to achieve optimal results.