Meta-analysis of laboratory studies predicts large changes in phytoplankton communities in an acidifying ocean

Many studies have attempted to predict the consequences of climate change on the ocean's primary producers. While attempts to synthesize studies of the effects of temperature increase on phytoplankton have been relatively common, we are unaware of any similar effort related to the "other CO2 problem" of ocean acidification. Here we extract data from 40 manuscripts in which unialgal phytoplankton cultures were grown under either low-ambient CO2 concentrations or else elevated CO2 near levels predicted for year 2100. Phytoplankton responses to CO2 enrichment were quite variable between studies, and different strains could be positively or negatively affected under future concentrations. There was a significant difference between the CO2 response of different functional groups: eukaryotes and Prochlorococcus were roughly equally likely to be positively or negatively impacted, whereas most other cyanobacteria, including diazotrophs, were strongly enhanced under future conditions. Dynamical ecological simulations incorporating these observations suggest that the impact of CO2 on growth rates alone will be sufficient to profoundly alter the distribution and relative abundance of the major phytoplankton functional groups by 2100, with potential profound impacts on the ecosystem services of the World Ocean.