Costs and benefits of calcification in coccolithophorids

Calcification in coccolithophorids requires major intracellular fluxes of inorganic carbon and calcium. This paper summarises the major cellular fluxes of substrates and products of calcification described in a simple four compartment model (cytosol, Golgi, coccolith vesicle and chloroplast). Measurements of the cytosolic and intra-coccolith vesicle pH and electrical potentials across the plasma membrane and coccolith vesicle membrane allow calculations of the proton electrochemical gradients across these membranes and estimates of the free carbonate and calcium concentrations in the coccolith vesicle. Calcification may provide a relatively low cost route for elevating the concentration of carbon dioxide in the chloroplast. This may have benefits in terms of the nutrient requirements for photosynthesis and growth. In particular, a close relationship appears to exist between calcification and the availability of phosphorus which may correlate with the occurrence of large scale blooms of Emiliania huxleyi in the North Atlantic.