Climate change in the rocky intertidal zone: predicting and measuring the body temperature of a keystone predator

Forecasting the responses of populations and ecosystems to climate change requires that we understand both the direct effects of temperature on organism physiology and the indirect effects of temperature change on interactions such as predation and competition. The sea star Pisaster ochraceus is a keystone predator in the rocky intertidal zone with a broad geographic distribution along the west coast of North America. We developed a mechanistic heat budget model that uses environmental data to predict the body temperatures of P. ochraceus. Model accuracy was verified by comparing model output temperatures, generated using measured microclimatic data as input, to the temperatures of live P. ochraceus in the field. The average absolute errors between predicted and measured body temperatures were ~1°C. To continuously monitor sea star body temperatures in the field, we developed data loggers that thermally mimic P. ochraceus. Accuracy of these biomimetic loggers was tested by comparing logger temperatures to P. ochraceus body temperatures, and they were found to mimic body temperatures within ~1°C. Loggers were deployed at different tidal heights at a site in Bamfield, British Columbia, Canada, to investigate within-site body temperature variation. We also explored the relationship between body temperature and vertical distribution of P. ochraceus. A negative correlation was found between maximum body temperatures on Day n and the number of sea stars found in the intertidal on Day n + 1. These results suggest that temperatures reached during aerial exposure at low tide, at least in part, may determine where in the intertidal zone these sea stars are located, which could affect their foraging limits.