Date of Graduation

Summer 2016


Master of Science in Biology



Committee Chair

M. Chris Barnhart


The purpose of this study was to determine the upper thermal limits of unionids. Three species of juvenile freshwater mussels were tested in lab experiments mimicking a diel pattern of temperature change (increasing 6 h, peak 2 h, and decreasing 8 h). The peak temperature fatal to half of the exposed population (LT50) was tested with respect to species, population, age, and seasonal acclimation. Mortality was monitored for 2 weeks after exposure. The smallest size classes were tested in a thermal cycler instrument, a novel application for testing mussels. LT50s for juveniles less than 3 weeks old were within 2-3°;C higher or lower compared to juveniles 1-2 years older. LT50s for peak temperature in summer-acclimated mussels were 33.2, 39.1, and 38.9°;C for Western pearlshell, Fatmucket, and Washboard juveniles less than 3 weeks old compared to LT50s of 36.1 and 40.8°;C for Fatmucket and Washboard 1-2 years of age. These results are several degrees higher than previously reported for continuous temperature exposures lasting 1- several days. LT50s for summer acclimated mussels immersed in water were 2-3°;C higher than for those emersed in damp sand. LT50s for winter acclimated mussels immersed in water were 1°;C lower than those emersed in damp sand. Winter acclimated Washboard had LT50s 2-4°;C lower than summer acclimated animals. These data can be used to predict the impacts on threatened mussel species of increased temperatures resulting from anthropogenic factors including climate change.


Unionoida, LT50, temperature tolerance, thermal cycler method, Lampsilis siliquoidea, Megalonaias nervosa, Margaritifera falcata

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© Kathryn Rae Cottrell Martin

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