Variation in assemblages of freshwater mussels downstream of dams and dam removals in the lake michigan basin, Michigan, USA

Abstract

Impacts of barriers, including dam removals, on aquatic diversity are poorly understood. We assessed freshwater mussel assemblages and microhabitat downstream of uncontrolled and controlled low-head dams and low-head dam removals in Michigan, USA. The objectives of this study were to quantify whether downstream mussel assemblages and microhabitat parameters differ by anthropogenic barrier and along a downstream gradient, and to determine parameters that were predictors of mussel diversity and density. Sampling consisted of standardized timed-searches and quadrat excavations. Results suggest that areas downstream of dams had higher mussel diversity than dam removals, and mussel assemblages differed along a downstream gradient for uncontrolled and controlled dams. Indicator Species Analyses determined mussel species representative of downstream river reaches from uncontrolled low-head dams and removals. Predictor variables for mussel assemblages included substrate classes and total suspended solids. Controlled dams contained the least fine substrates (%) and highest coarse substrates (%) in downstream reaches. This study sug-gests that rivers with uncontrolled low-head dams and removals provide downstream habitat that support viable mussel assemblages. Results from this study also suggest that evidence of mussel assemblage recovery following dam removal may take many years. Quantification of barrier-re-lated impacts, as shown in this study, are imperative to guide conservation of aquatic fauna.