JOST, JA*; HELMUTH, BST; University of South Carolina; University of South Carolina: Thermal tolerance of Geukensia demissa: The effect of daily maximum temperatures on growth and mortality

Predicting alterations in communities due to climate change requires elucidation of both the physiological limits and the exposure ranges of organisms in the field. The Atlantic ribbed mussel, Geukensia demissa, is a dominant component of salt marsh ecosystems from the Gulf of St. Lawrence to Northeast Florida, an exposure gradient that would be expected to encompass temperatures from -20°C to above 50°C. Published laboratory studies indicate a tolerance range of �22°C to 40°C. However, since body temperature patterns in the field are not known, resolution of the discrepancy between expected field temperatures and published physiological limits is not currently possible. I have documented spatial and temporal patterns in the body temperature of the mussel Geukensia demissa by examining the effects of microhabitat, body size, and body position within the sediment in a South Carolina estuary for a period of two years. These data suggest that the upper lethal limit for this species is much higher than 40°C, and model body temperatures up to 51.5°C have been recorded. Using these field data, I developed a laboratory experiment to determine the effects of temperature on mortality and growth rate. Mussels were exposed to the same daily maximum temperature (ranging from 30-55°C) for a period of three months. Data suggest that 100% mortality occurs at 55°C, 75% mortality at 50°C, and <5% mortality at 30, 35, 40, and 45°C. Growth rate data suggests that mussel growth decreases with increasing maximum temperature. These data suggest that Geukensia demissa is living close to its thermal limits in Southern salt marshes. Therefore, there is a potential for mussel mortality with global climate change, leading to changes in salt marsh community structure.