Elevated CO2 Effects in the Coccolithophore Emiliania huxleyi (Prymnesiophyceae)

DOI: 10.1111/jpy.12885

¹ Department of Ecology, Faculty of Sciences, University of Málaga, Bulevar Louis Pasteur s/n, Málaga 29071, Spain

² Smithsonian Environmental Research Center, 647 Contees Wharf Rd, Edgewater, MD 21037, USA

³ Department of Ecology and Animal Biology, Faculty of Sciences, University of Vigo, Campus Lagoas-Marcosende. 36310 Vigo, Spain

⁴ Marine Scotland Science, Marine Laboratory, 375 Victoria Road, Aberdeen, AB11 9DB, U.K

We studied the effects of elevated CO₂ concentrations on cell growth, calcification and spectral variation in the sensitivity of photosynthesis to inhibition by solar radiation in the globally important coccolithophore Emiliania huxleyi. Growth rates and Chl a content per cell showed no significant differences between elevated (800 ppmv) and ambient (400 ppmv) CO₂ conditions. However, the production of organic carbon and the cell quotas for both, carbon and nitrogen, increased under elevated CO₂ conditions whilst particulate inorganic carbon production rates decreased under the same conditions. Biometric analyses of cells showed that coccoliths only presented significant differences due to treatments in the central area width. Most importantly, the size of the coccosphere decreased under elevated CO₂ conditions. The susceptibility of photosynthesis to inhibition by ultraviolet radiation (UVR) was estimated using biological weighting functions (BWF_S) and a model that predicts photosynthesis under photosynthetically active radiation (PAR) and UVR exposures. BWF results demonstrate that the sensitivity of photosynthesis to UVR was not significantly different between E. huxleyi cells grown under elevated and present CO₂ concentrations. We propose that the acclimation to elevated CO₂ conditions involves a physiological mechanism of regulation and allocation of energy and metabolites in the cell, which is also responsible for altering the sensitivity to UVR. In coccolithophores this mechanism might be affected by the decrease in the calcification rates.