Emersion and thermal tolerances of three species of unionid mussels: Survival and behavioral effects

We evaluated the behavior and survival of unionid mussels after emersion in air temperatures across a range that is likely to be encountered during status surveys or relocations. Five laboratory tests were performed with pocketbook Lampsilis cardium Rafinesque (2 tests), pimpleback Quadrula pustulosa Lea (1 test), and spike Elliptio dilatata Rafinesque (2 tests) mussels, each conducted in a completely randomized, nested experimental design. For each mussel species (except Q. Pustulosa), treatments tested included two water temperatures (25 and 10 degrees C), five air temperatures (ranging within +/-20 degrees C of the water temperature), three aerial exposure durations (15, 30, and 60 min), and a no emersion control. All treatments were duplicated, with 10 organisms per emersion time and aerial exposure temperature (n = 320 mussels per test). Behavioral response (ability to upright) and mortality were measured daily for 14 d postemersion. Both water and aerial exposure temperature (air shock) were important predictors of times to first uprighting. The intensity function of first uprighting differed among species (P < 0.01), and there was a significant interaction between E. Dilatata versus the other species and water temperature (P +/- 0.01). Over-all mussel survival after emersion was high (93%); however, E. Dilatata experienced significant treatment related mortality at the 25 degrees C test water, 45 degrees C aerial exposure temperature. Because of the high incidence of uprighting and survival of mussels in our study, emersion at moderate temperatures (15 to 35 degrees C) and durations (15 to 60 min) does not seem harmful to mussels, and, therefore, conducting relocations and status surveys under these conditions should not impair mussel survival and over-all success.