Use of metabolic assays to assess thermal and hypoxia stress of freshwater mussel species from central Texas

Abstract

Warming temperatures are a major concern for freshwater mussels as they are limited in range, mobility, and potential to seek refuge from heat stress. Unionid mussels are ectothermic organisms, and the temperature of their immediate environment strongly influences their metabolism. We used metabolic assays at both the organismal and cellular level to assess potential effects of thermal stress and hypoxia on freshwater mussels from central Texas. At the organismal level, as measured via closed respirometry, metabolic rates increased with increasing temperature for all taxa, but the shape and slope of the relationship were variable among species and subpopulations. Sensitivity to hypoxia with rising temperature was only found in two of the taxa tested. Enzymatic thermal optima and potential metabolic activity varied among taxa tested with chronic and acute heat stress. Effects of temperature acclimation on respiratory enzymes were variable as well, revealing potential differences in adaptations between species and subpopulations.