Abstract
Coral reefs experience biologically-driven pCO(2) oscillations that are predicted to become more extreme in magnitude and duration under ocean acidification (OA) regimes. Understanding the plasticity of responses in common reef-building corals to oscillations in pCO(2) will allow for better predictions of their function in future seawater conditions. This study explored the effects of variation in seawater pCO(2) on coral calcification using experiments conducted over one month between 9 April 2018 and 18 May 2018. Branches (similar to 4-cm long) of Acropora retusa were sampled from colonies at 10-m depth on the fore reef of Mo'orea, French Polynesia (17 degrees 28' 53.9004 '' S, 149 degrees 49' 50.5992 '' W). We tested the hypothesis that depressed calcification caused by elevated pCO(2) (similar to 1000 mu atm) is relaxed (i.e., calcification increases) upon return to ambient pCO(2) (similar to 400 mu atm). Corals first were incubated in ambient or elevated pCO(2) for 19 days, with the result that calcification integrated over this period was reduced by 31% under elevated pCO(2). The same corals were then incubated at ambient pCO(2) for 11 days, during which calcification was independent of the experimental pCO(2) exposure history. Our results suggest that a quick relaxation of pCO(2)-depressed calcification in A. retusa following cessation of high pCO(2) indicates that corals are capable of a reversible plastic response of calcification when confronted by pCO(2) oscillations.