MEPS 601:59-76 (2018)  -  DOI: https://doi.org/10.3354/meps12639

ABSTRACT: 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 pCO₂ (between 250 and 750 µatm) 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 pCO₂ on dark calcification. Increased pCO₂ conditions had no significant impact on P. carterae growth rate or photosynthetic rate. However, P. carterae calcification rates significantly increased at elevated mean pCO₂ concentrations of 750 µatm. P. carterae calcification was somewhat, but not completely, light-dependent, with increased calcification rates at elevated mean pCO₂ conditions in both light and dark incubations. This trend of increased calcification at higher pCO₂ 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 pCO₂ on coccolithophore calcification.

KEY WORDS: Ocean acidification · Coccolithophore · Calcification · Carbon dioxide · CO₂ · Photosynthesis · PIC:POC ratio · Pleurochrysis carterae