Ocean acidification effects on calcification in Caribbean scleractinian coral exposed to elevated pCO2: a potential for acclimation

Ocean acidification (OA) is projected to increase the acidity of coral reef habitats 2-3 times that of present day pCO₂ levels. Many studies have shown the adverse effects on scleractinian calcification when exposed to elevated pCO₂ levels, however, no such effects were seen in this study whereby corals were exposed for three months to elevated pCO₂ levels. In this study, all corals were kept in culture for one year prior to being used in experimental trials. Data from culture systems shows coral experience a range of pCO₂ from 300-600 µatm over the course of a day. This range is attributed to respiration and photosynthesis which also naturally occurs in a reef habitat. Montastrea cavernosa, Orbicella faveolata, and Pseudodiploria clivosa were exposed to their ambient culture conditions (control) or to elevated pCO₂ levels of 1000 µatm (IPCC A1F1 scenario). By combining photographic analysis of live tissue area or exposed skeleton with the buoyant weight technique, an area density of each coral fragment was obtained to infer rates of calcification or erosion of skeleton. After three months of experimental exposure, preliminary results suggest that there is no significant difference in calcification or erosion in any of the species tested. Acclimation in the elevated pCO₂ culture environment may have conditioned the coral to better withstand high pCO₂ levels. Long acclimation periods of coral to near term future pCO₂ levels may more accurately predict calcification responses in corals of the future.