Seasonality in calcification response of Hawaiian reef coral, Montipora capitata, under climate change projections

The response of coral reef communities to future environmental conditions is a topic of enormous concern and considerable debate. However, information is lacking concerning the interaction between local and global stressors on modern reefs. Irradiance and temperature, along with other numerous environmental factors that regulate coral calcification rates and productivity, are predicted to change with future elevated carbon dioxide (CO₂) emissions. Therefore, an experiment was performed in continuous flow mesocosms under full solar radiation to describe the direct and interactive effects of temperature, irradiance, and pCO₂ on the calcification of the Hawaiian reef building coral, Montipora capitata across seasonal and temporal scales. Corals were subjected to twelve experimental treatments composed of two pCO₂ levels (present day levels, 2X present), two temperature regimes (ambient, heated +2°C), and three conditions of irradiance (ambient, 50% and 90% reduction). Results revealed irradiance and temperature stress have the strongest influence on coral calcification with pCO₂ playing a lesser role. The effects of pCO₂ also varied among temperature and irradiance regimes. Large decreases in calcification were observed in corals under ambient irradiance levels that were exposed to elevated temperatures and high pCO₂ levels. These results suggest the interaction of these environmental parameters may alter optimal growth conditions of M. capitata under future climate change projections.