Lethal and Sublethal Effects of Water Temperature on Native Mussels: Implications for Climate Change Research

Native freshwater mussels are a diverse, but imperiled fauna and may be especially sensitive to increasing water temperatures because of their patchy distribution, limited mobility, limited dispersal, larval dependence on a host fish, and the fact that they already inhabit fragmented landscapes.  Recent research suggests that many mussel species may currently be living near their upper thermal limits.  We tested the hypothesis that elevated water temperatures (20, 25, 30, and 35°C) will adversely affect the survival and physiology of juvenile and adult mussels in laboratory tests.  In juveniles, the 28-d LT50’s (lethal temperature affecting 50% of the population) ranged from 25.3 to 30.3°C across 3 species.  Mortality of 4 species of adults was minimal.  In general, heart rate, but not growth rate, was significantly affected by temperature in juveniles, but the magnitude of these effects was small.  Preliminary analyses suggest that metabolic processes (i.e., rates of oxygen consumption and nitrogen excretion) in adults were also affected by temperature.  These data are being used in a downscaled global climate change model to forecast species responses to climate change and to develop strategies to mitigate adverse effects.