Do Density and Food Availability Influence Survivorship and Reproduction in the Freshwater Bivalve, Sphaerium simile?

The small freshwater bivalve Sphaerium simile, like most “fingernail clams” (Sphaeriidae), does not exhibit a planktonic larval stage but instead offspring are brooded inside the valves of the parent. The species is generally regarded as reproductively specialized, or relatively “K” selected along the r‐K continuum. Multiple offspring can develop simultaneously, but brooding siblings are commonly at different developmental stages. An experiment was conducted to evaluate the relative success of brooding offspring and adults in different adult densities and feeding regimes. A controlled laboratory experiment examined four treatment groups, with adult density and feeding frequency as independent variables. There were two density treatments [0.07 (low) and 0.35 (high) clams per cm2] and two feeding treatments (continuous and once each week). A parallel field experiment was conducted with high, moderate and low density treatments. In the laboratory experiment, offspring production was highest in treatment groups with high densities and/or more frequent feeding. Mortality of adults was highest among subjects kept at low feeding frequency feeding. In the field experiment, offspring production was highest in high and moderate density treatments. These results provide insight into the life history and stress response of Sphaerium simile, a brooding bivalve that remains under studied