Downstream transport and seasonal variation in freshwater pearl mussel (Margaritifera margaritifera) eDNA concentration

Abstract

Environmental DNA (eDNA) can be used to detect the presence and abundance of aquatic organisms from water samples. Before implementing this methodology as a tool for monitoring, more knowledge is needed on variation in eDNA concentrations in relation to species abundance and potential confounding factors. Shedding and decay of eDNA may vary extensively over the season and are dependent on environmental factors such as water temperature and on biological processes such as activity level and reproduction. In lotic systems, eDNA concentrations are also affected by downstream transport of eDNA. Sessile freshwater mussels provide an ideal study system for investigating the relationship between species spatial distribution and eDNA concentrations in lotic systems. We quantified freshwater pearl mussel (Margaritifera margaritifera) eDNA concentrations at four localities in a natural river with detailed knowledge of mussel spatial distribution: (a) upstream of the known species distribution, just downstream (b) a small and (c) a large aggregation and (d) 1,700 m downstream of the large aggregation. To study seasonal variation, we quantified eDNA concentrations during three periods: (a) in late spring, with cold water and relatively inactive mussels; (b) in mid-summer, with higher water temperature and active mussel filtration; and (c) in late summer, during the release of larvae.Species detection was highly reliable, with no detection of eDNA upstream of the species distribution and complete detection downstream of the large aggregation.Detection success of the small aggregation was low, with 13% of the samples testing positive. Downstream transport was efficient, with no significant decrease in eDNA concentrations over 1,700 m river distance. Seasonal variation was strong, with a 20-fold increase in eDNA concentrations from late spring to late summer, during reproduction. Our results highlight both the potential and challenges of eDNA monitoring in lotic systems. K E Y W O R D Sconservation genetics, environmental DNA, freshwater mussels, species detection, unionidae | 65 WACKER Et Al.

Detection of an invasive aquatic plant in natural water bodies using environmental DNA

“…These rates must be seen as first estimations to guide more detailed studies as for other organisms. In two other studies, eDNA from freshwater mussel beds (sessile organism) were detected 1000m downstream in a mesocosm [18] and 1700m downstream of a natural large aggregation [68], which is in the same range as the 1400m found in this study.…”

Assessing the impact of the threatened crucian carp (Carassius carassius) on pond invertebrate diversity - a comparison of conventional and molecular tools

“…Mollusca), ectoparasites (i.e. Acari) that feed on blood or skin of other species, or use external versus internal fertilisation (Mächler et al, 2019;Wacker et al, 2019). Furthermore, species may differ in their habitat preferences and utilisation, potentially resulting in highly localised distributions (Klymus et al, 2017;Mächler et al, 2019).…”

Using environmental DNA (eDNA) to detect the endangered Spectaclecase Mussel (Margaritifera monodonta)

“…Stoeckle et al (2016) failed to detect M. margaritifera DNA 500 and 1000 m downstream from the mussel beds, whereas Deiner and Altermatt (2014) were able to successfully amplify Swollen River Mussel (Unio tumidus [Philipsson, 1788]) DNA 12 km downstream from the lake the species inhabited. Even though M. monodonta reside in sheltered habitats, it is possible that their eDNA is transported efficiently downstream in river systems, as has been suggested for M. margaritifera (Wacker et al 2019). We observed only a marginal decrease in detections out to 500 m, but we suspect that if we had continued sampling farther downstream (e.g., 1-2 km) at the St Croix site B and the UMR pools 15 and 16 sites, then we likely would have observed a substantial distance effect with reduced detections at longer distances from the source population.…”

“…Of these invertebrate eDNA studies, little focus has been on rare, threatened, or endangered species. The sensitivity of eDNA methods to detect low-density populations of benthic-dwelling organisms in a flowing system has only recently been demonstrated (Deiner and Altermatt 2014, Stoeckle et al 2016, Carlsson et al 2017, Dyer and Roderique 2017, Hu 2017, Currier et al 2018, Roderique 2018, Schill and Galbraith 2019, Wacker et al 2019. Relative to fish, mussels may shed less DNA because they can close their valves, are smaller in size and biomass, and generally have a restricted portion of soft tissue (i.e., the mantle and siphons) exposed to the water column (Takahara et al 2012, Thomsen et al 2012, Sassoubre et al 2016, Sansom and Sassoubre 2017.…”