MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14802

ABSTRACT: Vulnerability to warming temperatures under climate change arises when there is a gap between local climate and local physiology. Intertidal species are unique because they face two distinct thermal environments, and it is unclear which is the bigger driver of thermal physiology and vulnerability. Here we compare the thermal environments and physiology of three populations of the intertidal barnacle Balanus glandula, spanning 1460 km of its geographic range. We measured energy consumption in the laboratory across a 5-hour emersion and subsequent 6-hour immersion at 7 different emersion temperatures (10-38°C). We compared these results to one year of emersion and immersion temperature data from each location. Our results suggest that the temperatures experienced during emersion are a bigger driver of each population’s thermal physiology than those experienced during immersion. We also estimated vulnerability to future warming in two ways: as the total annual energy demand and as the number of days above each population’s thermal peak. These produced conflicting results. The central population spent the most days over its thermal peak, but the northernmost population had the greatest total costs over a year. This discrepancy suggests that different aspects of B. glandula’s thermal performance may be under selection from different aspects of the environment. Thus, accurate predictions of B. glandula’s response to warming temperatures will require knowledge of both future temperature and food availability.