Intraspecific variation in the response of the scleractinian coral Acropora digitifera to ocean acidification

To examine the possible variation in responses of corals to ocean acidification (OA) among populations, we compared the sensitivity of two Okinawan populations (Sesoko and Bise) of the scleractinian coral Acropora digitifera to high pCO2. We found that both light and dark calcification rates of Sesoko corals did not change with an increase in seawater pCO2, while the calcification rates of Bise corals significantly decreased. Additionally, calcification rate of Sesoko corals was significantly lower than Bise corals at control conditions. Expressions of two putative calcification-related genes (BAT: bicarbonate transporter and galaxin) were up-regulated at high CO2 compared to the control and expression of the BAT gene was significantly higher in Sesoko compared to Bise corals. Consequently, differences in the calcification rate between populations and differences in the expression of genes related to inorganic carbon transport regulation could be reasons that explain the difference in the response to OA between the two populations. Furthermore, taking into account that Sesoko corals were located in relatively nearshore areas where the environmental conditions are more variable, while Bise corals were located in the forereef which shows more stable conditions, plasticity for coral calcification in response to different environmental conditions and/or acclimation response to changes such as seawater pCO2 may lead to differences in sensitivity between the two populations to high seawater pCO2. Studies considering the potential variability in corals sensitivity to OA among local populations from different habitats are important to predict the potential effects of climate change on reef ecosystems.