FITZHENRY, Tara; GARDNER, Kristi; HELMUTH, Brian: The steamy side of intertidal life: do Mytilus californianus gape to evaporatively cool?

Rocky intertidal mussels Mytilus californianus can be exposed to potentially damaging thermal conditions during low tide. One potential mechanism for alleviating the effects of thermal stress is to evaporatively cool by gaping, a behavior that also may occur during aerial respiration. However, the relationship between body temperature and gaping behavior has never been fully demonstrated for this species. We exposed mussels to a range of temperatures under several experimental treatments. Results suggest that there is no significant relationship between mussel gaping and temperature. Mussels that were observed gaping showed little or no reduction in body temperature as their temperatures did not vary greatly from those of non-gaping neighbors. In several instances mussels expired without showing any signs of evaporative cooling. These results, while preliminary, suggest that gaping behavior in this species may be more strongly related to aerial respiration than to body temperature. In order to estimate temperatures in the field in the absence of evaporative cooling, we deployed a series of temperature loggers that were designed to thermally match live mussels (similar size, morphology and thermal inertia) at two sites in central Oregon (Boiler Bay and Strawberry Hill). Tests comparing these loggers to real mussels suggest that thermally-matched loggers record temperatures that are within a few degrees of real animals, and are considerably more accurate than unmodified loggers. Mussel logger temperatures at these sites reached maxima of 35�-40�C or greater, close to the predicted thermal tolerance of this species. Supported by NSF IBN-9985878 to BH.