Modulation of near-bed hydrodynamics by freshwater mussels in an experimental channel

Freshwater mussels are important ecosystem engineers, and recent studies have illustrated their many ecological contributions, but little is known about the interaction between mussels and their surrounding flow environment at the organism scale. In the present experimental campaign, we examine the hydraulic interactions between mussels and open-channel flow. We quantify how a mussel-covered bed alters bed roughness and near-bed turbulent flow, determine the filter behavior and capacity of live Lampsilis siliquoidea, and design a model mussel to simulate live mussel filtering to examine the impact of the biologically mediated activity of filter feeding on near-bed turbulent flow. In comparison to a gravel bed, a mussel-covered bed increased shear velocity by 28% and bed roughness by nearly 300%, and significantly reduced near-bed flow velocity. The filter velocity in L. siliquoidea varied within and between individuals, and ranged from 0.4 to 20 cm/s. The excurrent flow of the model mussel accurately simulated excurrent flow observed in live mussels and, when subjected to various boundary conditions, altered water velocity and turbulent kinetic energy downstream. The ability to describe and quantify these hydrodynamic interactions provides new insight into how mussels modulate near-bed flow and mixing processes, which can contribute to future conservation efforts.