MEPS 502:145-156 (2014)  -  DOI: https://doi.org/10.3354/meps10720

ABSTRACT: Fragments of 2 coral species (Acropora nasuta and Pocillopora damicornis), collected from the South China Sea, were incubated for 94 d under controlled conditions of pCO₂ = 389, 700, and 1214 µatm. Our incubation experiments showed that the net calcification rate of A. nasuta responded negatively to elevated pCO₂ in both short and mid-term incubations. In contrast, the net calcification rate of P. damicornis increased under elevated pCO₂ during the first 17 d, but then returned to background rates. Based on previous models, our modified models showed that the different responses of these 2 coral species depended on the dissolved inorganic carbon (DIC) and pH levels in coral calcifying fluid. In the studied models, the positive responses of coral calcification to higher pCO₂ could be explained by either low DIC due to a higher photosynthesis rate or a stronger H⁺ pump. If DIC in calcifying fluid is greatly reduced by photosynthesis, the decreased DIC in calcifying fluid may be benefited by enhanced external seawater CO₂, which will partially offset the dissolution due to ocean acidification. Therefore, in addition to our experimental results, our model provides a theoretical basis showing how coral may respond negatively and positively to ocean acidification.

KEY WORDS: Coral calcification · Ocean acidification · Dissolved inorganic carbon · pH · Modelling