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

The interaction between photosynthesis and calcification remains poorly kno wn in zooxanthellate scleractinian corals. We tested whether calcification is a significant source of CO2 for photosynthesis in Stylophora pistillata. Rates of net photosynthesis, respiration, add calcification were measured on colonies incubated in synthetic seawater (SSW) controlled with respect t o the inorganic carbon system and containing standard (11.40 mmol kg(-1)) a nd low (2.85 mmol kg(-1)) calcium concentrations. Net photosynthesis and re spiration are not significantly different in standard and low-Ca2+ SSW desp ite a rate of calcification 2.0-2.4 times lower in Ca2+-depleted SSW. Addit ional 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 ca lcification is not a significant source of photosynthetic CO2 and that phot osynthesis stimulates calcification rather than the opposite.