This talk is part of the Marine Ecosystem and Climate series. Stephanie Dutkiewicz will present some of her new modelling work.

Abstract

The world's oceans have absorbed about 30% of anthropogenic carbon emissions, causing a significant decrease in surface ocean pH. Concerns over the impacts of this “ocean acidification” to marine life have led to a number of laboratory, mesocosm, and field experiments. The most publicized studies concern calcifying organism such as corals and bivalves (e.g. oysters and mussels). However ocean acidification will also affect phytoplankton: the microscopic photosynthesizing organisms that form the foundation of the marine food web and regulate key biogeochemical processes, including the cycling of carbon. Here we provide results from a meta-analysis of experiments that assessed growth rates of different phytoplankton taxa under both current day and elevated pCO2 conditions. These results revealed a significant range of responses. We use a numerical model to explore how these responses at the laboratory scale might scale up to the community and global level. In simulation over a hypothetical 21st century we found that ocean acidification caused sufficient changes in competitive fitness between phytoplankton types to significantly alter community structure. We compared the impact of ocean acidification to other potential stressors of phytoplankton communities (such as warming, and changes to the light environment and nutrient supplies) and found that it will likely have a greater impact at the level of ecological function of the phytoplankton community. Our results suggest that longer time scales of competition- and transport-mediated adjustments are important in predicting the changes to phytoplankton community structure; aspects that are not captured in laboratory or field experiments. Including these effects are essential for our understanding of the future of the marine ecosystem: the large turnover of community functionality suggested by our model could carry profound consequences for all levels of the marine food chain as well as global biogeochemistry.