Intraspecific variation in response to elevated pCO2 and temperature in the branching reef coral Acropora digitifera from different habitats

Ocean acidification (OA) and ocean warming (OW) affect the calcification of corals, and intraspecific variations in response to these stressors in the population level need to be clarified for better future predictions. Using Acropora digitifera as our subject, we examined the intraspecific variability in calcification and maximum quantum yield (F_v/F_m) of photosystem II of symbiotic zooxanthella in responses to OA, OW, and OA + OW. Samples were taken from two different sites: Sesoko Station (warmer) and Sesoko South (cooler) in Okinawa, Japan. Calcification rates varied between the two sites, and noticeable differences were observed only among coral colonies from the Sesoko South site, specifically under control and OA treatments. Furthermore, F_v/F_m showed no variation between the sites due to those stresses. Hence, the calcification rates among A. digitifera colonies varied by habitat, and we found within-site variation only in the lower temperature location, Sesoko South. We observed diminished variation in response among colonies in the warmer site. The adapting to diverse environmental conditions and responding to changes such as seawater pCO₂ and temperature, may lead to differences in sensitivity between the two populations to OA, OW, and OA + OW. These intraspecific variation could arise from factors like acclimatizations, the influence of specific genotypes, or phenotypic plasticity of the colonies.