The response of marine picoplankton to ocean acidification

Since industrialization global CO2 emissions have increased, and as a consequence oceanic pH is predicted to drop by 0.3-0.4 units before the end of the century a process coined ocean acidification. Consequently, there is significant interest in how pH changes will affect the ocean's biota and integral processes. We investigated marine picoplankton (0.2-2 mu m diameter) community response to predicted end of century CO2 concentrations, via a high-CO2 (similar to 750 ppm) large-volume (11 000 l) contained seawater mesocosm approach. We found little evidence of changes occurring in bacterial abundance or community composition due to elevated CO2 under both phytoplankton pre-bloom/bloom and post-bloom conditions. In contrast, significant differences were observed between treatments for a number of key picoeukaryote community members. These data suggested a key outcome of ocean acidification is a more rapid exploitation of elevated CO2 levels by photosynthetic picoeukaryotes. Thus, our study indicates the need for a more thorough understanding of picoeukaryote-mediated carbon flow within ocean acidification experiments, both in relation to picoplankton carbon sources, sinks and transfer to higher trophic levels.