HELMUTH, B.; GILMAN, S.; WETHEY, D.S.; Univ. of South Carolina, Columbia; Univ. of South Carolina, Columbia; Univ. of South Carolina, Columbia: Predicting biogeographic responses to climate change in rocky intertidal ecosystems: a mechanistic approach
Intertidal organisms are often assumed to live close to their thermal limits, and thus have emerged as potential early indicators of the effects of climate change on natural ecosystems. Yet, patterns in body temperature during low tide are often counterintuitive because of the interactive effects of climate, tidal regime, and organism characteristics on heat flux. Using instruments designed to match the thermal characteristics of rocky intertidal mussels and barnacles, we have recorded temperatures over a wide range of spatial and temporal scales along the Pacific coast of the United States. Using a series of heat budget models we can furthermore accurately reproduce patterns in mussel and barnacle body temperature to within a few �C using climate data from local weather stations. Results of these simulations confirm that while water and air temperature serve as important environmental drivers of animal body temperature, neither is sufficient as a proxy for animal temperature. For example, whereas maximum air temperatures are, on average, 7-8�C different from maximum body temperature, our model predictions generally have an error of only 2.5�C. Analyses of elasticity (the proportional change in body temperature relative to change in environmental input) show that responses to body temperature are less than 1 for both air and water temperature. That is, a 1�C increase in air temperature always causes less than a 1�C increase in maximum body temperature. Importantly, however, elasticity changes with tidal height and between sites along the west coast. Our results thus suggest that responses to climate change in rocky intertidal ecosystems will be highly site-specific, and that the relative importance of air and water temperature as drivers of intertidal body temperature varies between sites.
