Suspended solid concentration reduces feeding in freshwater mussels

Abstract

We examined the effect of TSS concentration on the clearance rates (CR) of newly transformed juvenile and adult Lampsilis fasciola, L. siliquoidea, Ligumia nasuta, and Villosa iris, as increased total suspended solids (TSS) are thought to interfere with feeding processes. Mussel CR were measured in aerated (or swirled for juveniles) chambers at TSS concentrations up to 15mgL−1 for laboratory-transformed juveniles, and up to 100mgL−1 for adult mussels. The CR of one-week old animals increased with TSS concentration, likely due to ontological differences in feeding (pedal vs. suspension feeding) and gill development, but CR decreased monotonically with TSS concentration in older animals (two-, three- and four-week old juveniles). The CR of adult mussels were significantly lower at TSS concentrations ≥8mgL−1, which represented a threshold in CR. Although this threshold occurred at similar concentrations across the four species, the decline in CR was largest in L. fasciola (46% compared to no-TSS control), and smallest in V. iris (21%). Differences among species are likely related to differences in the TSS and substrate found in their source rivers given that greater decline occurred for species in rivers with relatively lower TSS. The decrease in CR as TSS increased is consistent across marine and freshwater bivalves, at both juvenile and adult stages. The decrease in feeding was five times greater in juvenile compared to adult bivalves, which indicates how the vulnerability to environmental stressors differ across life stages. These results demonstrate that TSS reduces suspension feeding rates in freshwater unionids, therefore TSS should be managed to ensure their survival.