Anthropogenic CO₂ emission have been increasing exponentially, leading to ocean acidification (OA) and warming (OW). By the end if the 21^st century, the concentration of CO₂ could exceed 1,000 matm and seawater temperature could rise by up to 3 °C. OA and OW are major global threats to coral reef ecosystems, as they reduce calcification rate of the corals. The effects of OW may be more severe when corals are simultaneously exposed to OA (OA+OW), with potential responses being additive, synergistic, or antagonistic. We conducted several comprehensive studies to investigate both inter-and intraspecific variation in the response of corals to OA, OW, and OA+OW. Our results indicated that the calcification rates of coral species decreased with increasing seawater pCO₂ and temperature. However, response patterns to OA, OW, and OA+OW differed among coral species (interspecific variation). Additionally, significant intraspecific variation was observed, with calcification rate varying among individual coral colonies. Interspecific variation can be attributed to differences in the calcification rate and endosymbiont diversity, while intraspecific variation is likely due to genetic differences among host corals. Our findings also suggests that OA reduced calcification rate by affecting the host corals, whereas OW decreases density, chlorophyll content, Fv/Fm by affecting the endosymbionts. The effects of OA+OW can be additive or synergistic, likely because OW and OW mainly acted on host corals and endosymbiont, respectively. In future high pCO₂ scenarios, corals may be more adversely affected by the combined impact of OA+OW than by either factor alone. OW appears to be the main stressor for reduced calcification and mortality, with OA serving as a secondary stressor in some coral species.

Ocean acidificcation,Ocean warming,Coral,Intraspecific,Interspecific