Suspended particulates decline along a dense, small-stream mussel bed

Jillian Fedarick , Daniel J. Hornbach, Bernard E. Sietman

Water filtration by freshwater mussels is a valued ecosystem service; however, it has not been well studied in natural settings. To examine the potential influence of mussel filtration on suspended particulates, we measured the concentration of Escherichia coli, chlorophyll-a, and total suspended solids along a stream reach with a dense mussel assemblage (Mussel Site) and a stream reach with no mussels (Reference Site). We predicted that these particulates would show greater declines along the Mussel Site than the Reference Site because of mussel filtration. We collected three replicate water samples at upstream, midpoint, and downstream stations at both sites in August, September, and October 2022 to measure concentration values. In accordance with our predictions, concentrations of particulates declined from upstream to downstream at the Mussel Site but not at the Reference Site. We used linear mixed-effect modeling to determine that the interaction between mussel presence (Mussel Site, Reference Site) and sample location (upstream, midstream, downstream) best explained these patterns. There was lower support for the total suspended solids interactive model (AIC weight = 0.45) compared to the other two particulates (AIC weight > 0.95). Selective feeding by mussels may help to explain the lower support of the total suspended solids model. Our results suggest that mussels can appreciably reduce suspended particulate concentrations including harmful bacteria. This study provides a useful example of the ecosystem services mussels provide and why their conservation is needed.