Calcification of an estuarine coccolithophore increases with ocean acidification when subjected to diurnally fluctuating carbonate chemistry

Ocean acidification has the capacity to impact future coccolithophore growth, photosynthesis, and calcification, but experimental culture work with coccolithophores has produced seemingly contradictory results and has focused on open-ocean species. We investigated the influence of pCO(2) (between 250 and 750 mu atm) on the growth, photosynthetic, and calcification rates of the estuarine coccolithophore Pleurochrysis carterae using a CO2 manipulation system that allowed for natural carbonate chemistry variability, representing the highly variable carbonate chemistry of coastal and estuarine waters. We further considered the influence of pCO(2) on dark calcification. Increased pCO(2) conditions had no significant impact on P. carterae growth rate or photosynthetic rate. However, P. carterae calcification rates significantly increased at elevated mean pCO(2) concentrations of 750 mu atm. P. carterae calcification was somewhat, but not completely, light-dependent, with increased calcification rates at elevated mean pCO(2) conditions in both light and dark incubations. This trend of increased calcification at higher pCO(2) conditions fits into a recently developed substrate-inhibitor concept, which demonstrates a calcification optima concept that broadly fits the experimental results of many studies on the impact of increased pCO(2) on coccolithophore calcification.