Abstract: The future response of marine ecosystem diversity to continued anthropogenic forcing is poorly constrained.  An extremely diverse set of organisms form the base of the marine ecosystem: phytoplankton. Currently, ocean biogeochemistry and ecosystem models used for climate change projections typically include only 2-3 phytoplankton types, and are thus too simple to adequately assess the potential for changes in plankton community structure.

Here we analyze a complex ecosystem model with 35 phytoplankton types to evaluate the changes in phytoplankton community composition, turnover and size structure over the 21st century. We find that the rate of turnover in the phytoplankton community becomes faster during this century, i.e. the community structure becomes increasingly unstable in response to climate change. 

Combined with alterations to phytoplankton diversity, our results imply a loss of ecological resilience, with likely knock-on effects on the productivity and functioning of the marine environment.