Meeting Abstract
During tidal cycles, intertidal animals may undergo large body temperature changes as exposure between water and air alternates. The California mussel Mytilus californianus (the dominant competitor for space on many shores) is a unique model for exploring how animals cope physiologically with extreme thermal stresses, as they cannot behaviorally respond (e.g. seek shade). As such, mussels can provide important predictive information about how climate change will affect other intertidal animals. Cardiac thermal tolerance, measured as the Arrhenius break temperature (ABT, temperature when heart rate abruptly declines) or flat-line temperature (FLT, temperature when the heart stops), is an excellent index for quantifying a mussel’s ability to cope with heat stress. Thermal tolerance tests entail heating mussels in air or water at constant rates until ABT and FLT occur. However, it is unknown whether heating rate (which varies widely in the field) independently affects ABT or FLT, and if mussels acclimatized to different intertidal heights respond differently. M. californianus from low- and high-zones (0.56 vertical m apart) were tested in air at various heating rates from 2.4 to 8.6 °C/h (spanning field measured rates), while measuring heart rate via infrared sensor. High- and low-zone mussels had similar ABT up until heating rates of ~5 °C/h, thereafter high-zone mussels’ ABT increased with heating rate while low-zone mussels’ ABT remained unchanged. FLT was unaffected by zone or heating rate. Overall, heating rate affects cardiac thermal tolerance in high- but not low-zone mussels. Therefore, heating rate needs to be accounted for during lab-based tests comparing mussels from differing intertidal zones, and more importantly when predicting the ecological consequences of our warming climate.
