Oxygen Flux Limitation drives Heat Wave Vulnerability of a Coastal Keystone Predator

Assessments of marine species vulnerability to ongoing climate change are often based on short-term experiments using unrealistic stressor scenarios, yet the opposite is needed to offer robust estimates. Here we subject a keystone predator, the sea star Asterias rubens, to projected warming and ocean acidification over a seasonal cycle. We show that warming and, less so, acidification, have pronounced impacts on animal energy budgets, albeit in a strongly season-specific manner. Simulated future summer temperatures can cause >95% sea star mortality and we can relate this mortality, as well as declining feeding rates at high temperatures to oxygen flux limitation. Using 15 years of field temperature data and end of century warming projections, we estimate that potentially lethal heat waves will occur in 20% of future years. Our study demonstrates the importance of assessing stress responses along seasonal thermal cycles to arrive with meaningful estimates of species sensitivity to climate change.