COS 82-1 - Impacts of temperature and CO2 on rocky shore ecosystems: results of a factorial field experiment

Abstract: As climate change continues and accelerates, our ability to prevent catastrophic impacts on ecosystem functioning is limited by an incomplete understanding of the effects of multiple climate stressors, especially in the context of an intact natural community. Most studies evaluating the effects of climate change on marine organisms have been conducted in laboratory or mesocosm settings, involve only single species in isolation, and include only one climatic factor (e.g., temperature alone or CO₂ alone). We conducted a 6-month factorial field manipulation of temperature and CO₂ in 20 rocky shore tide pools in southeastern Alaska, USA. We quantified population, community, and ecosystem impacts via community surveys and time-series sampling of pH and oxygen levels. The greatest impacts of our climate manipulations were precipitated through high mortality of shellfish and bleaching of algae which occurred at the uppermost edge of the intertidal gradient, where daily changes in temperature and acidity are greatest. The most extreme impacts were observed during a heat wave at our study site that occurred during the experiment. This suggests the existence of tipping points that can lead to mass mortality when climate change is added to extreme temperature and pH conditions in communities existing at the edge of species’ tolerance ranges.