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The increasing frequency and intensity of extreme climatic events demands a better understanding of how organisms respond to temperature shifts and how these responses shape species interactions. Temperature-related disruptions in individual behaviour and physiology can signal broader community change. This is particularly true for keystone species, whose impact on their ecosystem is disproportionately large. We tested how periodic exposure to high air temperatures affects mortality, feeding, and metabolism in juvenile Pisaster ochraceus (ochre sea star), a keystone intertidal predator, by manipulating air and seawater temperatures representing typical and heatwave conditions in Barkley Sound, British Columbia, Canada. To contextualize these findings, we also quantified local environmental temperatures paired with P. ochraceus body temperatures and physical condition in the field. We found the highest mortality (42%) in treatments exposed to cool seawater (~15°C) with high air temperatures (~30°C), which corresponded with ~50% reductions in both mussel consumption and metabolic rate. In contrast, warmer seawater (~20°C) mitigated these effects, supporting greater feeding and metabolic rates, even under high air temperatures (~30°C). These findings refute the assumption that a combination of warm seawater and high air temperatures would lead to greater cumulative heat damage. Thus, we predict that P. ochraceus will be vulnerable to heatwaves in spring and early summer when seawater temperatures remain cool. The timing of extreme heat events therefore plays a critical role in predicting species responses, particularly as warming air temperatures actively alter community dynamics by changing rates of keystone predation.
Walton et al. (Mon,) studied this question.