CO2 partial pressure controls the calcification rate of a coral community

Previous studies have demonstrated that coral and algal calcification is ti ghtly regulated by the calcium carbonate saturation state of seawater. This parameter is likely to decrease in response to the increase of dissolved C O2 resulting from the global increase of the partial pressure of atmospheri c CO2. We have investigated the response of a coral reef community dominate d by scleractinian corals, but also including other calcifying organisms su ch as calcareous algae, crustaceans, gastropods and echinoderms, and kept i n an open-top mesocosm. Seawater pCO(2) was modified by manipulating the pC O(2) of air used to bubble the mesocosm. The aragonite saturation state (Om ega(arag)) of the seawater in the mesocosm varied between 1.3 and 5.4. Comm unity calcification decreased as a function of increasing pCO(2) and decrea sing Omega(arag). This result is in agreement with previous data collected on scleractinian corals, coralline algae and in a reef mesocosm, even thoug h some of these studies did not manipulate CO2 directly. Our data suggest t hat the rate of calcification during the last glacial maximum might have be en 114% of the preindustrial rate. Moreover, using the average emission sce nario (IS92a) of the Intergovernmental Panel on Climate Change, we predict that the calcification rate of scleractinian-dominated communities may decr ease by 21% between the pre-industrial period (year 1880) and the time at w hich pCO(2) will double (year 2065).