Effects of Thermal Stress on Unionid Glochidia and Rising Salinity on Adult Unionid Mussels

Abstract

Unionid mussels are considered keystone species however, they are the most imperiled group of organisms in North America. Implications from changing thermal and salinity regimes are of particular interest due to potential negative effects on feeding, respiration, and reproduction. In this study, we investigated valve closure behavior of four mussels from central Texas in relation to rising salinity as well as respiratory patterns of Ligumia subrostrata glochidia at multiple viabilities and temperatures as dissolved oxygen (DO) declined from normoxic to hypoxic conditions. We found sensitivity to rising salinity varied among species and subpopulations. We found some species had a closure response to rising salinity indicating a cost/benefit associated with early vs delayed closure. Viability was found to have no influence on glochidia respiration rate, Regulation Index (RI), or critical dissolved oxygen criterion (DOcrit). However, temperature directly influenced all similar endpoints. We also estimated the percent of brooding female respiration rate comprised of brood oxygen demand could reach 12% depending on DO and temperature.