Calcification does not stimulate photosynthesis in the zooxanthellate scleractinian coral Stylophora pistillata

The interaction between photosynthesis and calcification remains poorly known in zooxanthellate scleractinian corals. We tested whether calcification is a significant source of CO2 for photosynthesis in Stylophora pistillata. Rates of net photosynthesis, respiration, and calcification were measured on colonies incubated in synthetic seawater (SSW) controlled with respect to the inorganic carbon system and containing standard (11.40 mmol kg-1) and low (2.85 mmol kg-1) calcium concentrations. Net photosynthesis and respiration are not significantly different in standard and low-Ca2+ SSW despite a rate of calcification 2.0-2.4 times lower in Ca2+-depleted SSW. Additional experiments carried out on the noncalcifying zooxanthellate Anthozoa Anemonia viridis demonstrate that a low calcium concentration has no direct effect on rates of photosynthesis and respiration. It is suggested that calcification is not a significant source of photosynthetic CO2 and that photosynthesis stimulates calcification rather than the opposite.