Unionid mussels are important constituents of aquatic systems that are affected by anthropogenic changes in hydrology and concomitant increases in suspended solids, yet little is known about the effects of flow on their suspension feeding. We examined the clearance rates (CRs) of four species of freshwater mussels (Lampsilis siliquoidea, Lampsilis fasciola, Ligumia nasuta, and Villosa iris) to determine whether they feed selectively on river seston and how this may vary with algal flux (concentration × velocity). The CR for the Lampsilis species was also determined using seston particle size, particle fluorescence, and algal taxon. The CR of all species increased linearly with flow chamber velocity, but exhibited saturation‐like kinetics with increasing algal flux. The CRs of Lampsilis species were higher for larger (>10 μm) versus smaller (<10 μm) particles, the latter of which were numerically dominant in river seston. The CR of Lampsilis mussels on most of the algal taxa declined (linearly or nonlinearly) with algal flux indicating that mussels have reduced ability to discriminate among algae at higher flux. This potential feeding limitation could affect mussel growth and survival and make unionids vulnerable to the aforementioned hydrological changes. Ecologically, differential use of algal taxa under different algal flux indicates selective feeding, which may be evidence of resource partitioning for mussel species that occupy the same rivers. The differential use of algal taxa under different algal flux within a mussel species indicates the complex nature of bivalve feeding, their habitat requirements, and their vulnerability to human impacts.

Despite their role as ecosystem engineers, which is in large part a consequence of their suspension feeding activities, the early life history of unionid mussels is not well understood. We examined the suspension feeding rates (i.e., clearance rates, CR) of recently metamorphosed juvenile Lampsilis siliquoidea (1-4 week old), Lampsilis fasciola (1-3 week old), Villosa iris (2 week old), and Ligumia nasuta (1 week old) under ecologically relevant flux conditions in a recirculating racetrack flow chamber system. The range of velocities examined was determined experimentally using a permeameter containing riverbed material (63 lm to 6.5 cm diameter) in which juvenile mussels are thought to reside. The CR of the juvenile unionid species increased linearly with algal flux and the ranking of CR among species was V. iris [ L. siliquoidea [ L. nasuta [ L. fasciola. CR also increased with the age (or size) of the mussel cohort but within a species CR increased non-linearly with shell length of the individual. These results provide new insight into the feeding abilities of recently metamorphosed juvenile mussels as well as potential threats to their growth and survival, which contributes to our understanding of their habitat requirements and may assist in the conservation of this imperiled taxon.