ADAPTABILITY OF KEY PHYTOPLANKTON SPECIES TO RAMPED OCEAN ACIDIFICATION: IMPLICATIONS FOR MARINE DIVERSITY AND THE GLOBAL CARBON CYCLE

Ocean acidification, the drop in oceanic pH as a result of increased atmospheric CO₂, poses a large threat to marine ecosystems globally. Recent laboratory studies have demonstrated the potential for adaptation in the coccolith producing phytoplankton Emiliania huxleyi, a major primary producer in marine systems that plays a significant role in nutrient transport and the global carbon cycle. Although laboratory culturing experiments have explored the physiological responses of E. huxleyi and other marine organisms to ocean acidification, the focus on short term responses has largely ignored the evolutionary potential for such organisms to adapt, while also not directly probing the effect that the rate of pH change has on adaptation ability. The present study examined the potential for adaptation of E. huxleyi to acidic conditions in a single clone multigeneration laboratory experiment. Cultures were exposed to treatments at ambient, elevated, and gradually ramped CO₂ levels. This experimental design allows us to examine the impact that incremental increases in CO₂, and thus decreases in pH, may have on the ability of E. huxleyi to adapt to ocean acidification. We tested for this ability by examining changes in growth rate as well as the production of organic and inorganic carbon per cell. These results may have implications for marine diversity and global carbon cycle processes under projected increases in atmospheric CO₂.