Bed shear stress as a predictor of juvenile unionid mussel settlement

Session: Physical Ecology in Large Lakes and Their Watersheds

Julian Lum, University of Guelph, [email protected]
Josef Ackerman, University of Guelph, [email protected]

Abstract

Freshwater mussels provide ecological services (e.g., nutrient cycling, water clarification) to the Great Lakes Basin, however 65% of them are At Risk. Mussel habitats are thought to be affected by hydrodynamics, which allow juvenile settlement to the streambed, and substrates, which provide physical support. The purpose of this study is to identify how hydrodynamic forces (e.g., bed shear stress) at the reach and local scale affect settlement and presence of juvenile mussels in the riverbed. We took high resolution riverbed elevation measurements to estimate reach-level shear stress via the depth slope product and identify possible locations where juvenile mussels exist.  At these candidate locations, local bed shear stress was measured using the law of the wall and excavated to find juvenile mussels via an airlift system. 49 stations were excavated; 40 within the Sydenham River, 9 within the Ausable River (Southern Ontario). Seven juvenile unionids were recovered in locations with relatively low measured local shear stress and smaller sediment size classes. The preliminary results are consistent with laboratory predictions that critical shear stress causes the incipient motion of juvenile mussels. These results help identify the habitats of juvenile unionid mussels and will aid in the recovery of these imperilled organisms.