P1.185 Wednesday, Jan. 4 Intertidal and subtidal Crepidula fornicata experiencing drastically different thermal conditions have similar physiological tolerances DIEDERICH, C.M.*; PECHENIK, J.A.; Tufts University; Tufts University email@example.com
For sessile marine organisms, the intertidal zone is a physically stressful environment at low tide, and thus a less favorable place to live than the adjacent subtidal zone. However, intense subtidal predation and competition force some species to live intertidally; individuals of those species are rarely found subtidally, and thus few studies compare the physiological tolerances of intertidal and subtidal conspecifics. In New England, dense populations of the gastropod Crepidula fornicata live both subtidally and intertidally. We characterized the tissue temperatures that intertidal and subtidal individuals of C. fornicata experienced throughout the summer by deploying biomimetic temperature loggers among living C. fornicata at -1.0 and +0.4 meters MLLW. We then determined the thermal tolerances of adults, lab-reared juveniles, and field-collected embryos, and the temperatures at which juveniles experienced heart failure. Intertidal animals experienced temperatures as high as 42°C, about 15°C higher than those experienced by subtidal conspecifics. However, most animals from both environments died following a 3 hour laboratory exposure to only 35°C, suggesting that intertidal individuals are living very close to their thermal maximum. Both intertidal and subtidal animals at all life history stages had similar thermal tolerances and showed little variability in lethal temperature; intertidal animals showed a decrease in thermal tolerance over two years of sampling. Thus, subtidal C. fornicata seem pre-adapted to cope with the thermal stresses associated with life in the intertidal zone. It is unlikely that either population is undergoing directional selection for higher thermal tolerance.