One of the greatest ecological, social and economic issues of the day is the problem of climate change. Increasing levels of carbon dioxide (CO2) in the atmosphere are increasing global temperatures. Much of the CO2 dissolves in the ocean, creating more acidic conditions and leading to a process known as ocean acidification (OA). Higher temperatures and increased levels of CO2 operating independently are known to be detrimental to corals, but little is known about their effect when operating in unison. Irradiance has a great influence on coral calcification rates and can interact with higher temperature and increased OA to an unknown extent. Therefore, experiments were performed in continuous flow mesocosms under various levels of solar radiation in order to describe the biological response of corals at the upper lethal temperature. Corals were grown under three conditions of irradiance (100%, 50% 8%), two pCO2 levels (present day levels and twice present) and various temperature regimes ranging up to the high temperatures that will occur during this century due to global warming. The results of this research indicate more rapid rates of bleaching in coral reefs under acidified conditions. During these experiments coral growth rates were suppressed under future climate change conditions, and high irradiance had the greatest effect on coral growth and bleaching. Temperature was more important than pCO2 in controlling growth. The interaction of temperature and irradiance had the strongest influence on coral growth rates. Therefore, low irradiance levels potentially provide a refuge for corals from thermal and irradiance stress in the deeper parts of their range. Coral health and mortality was observed to be influenced by the interaction of all three factors, while bleaching and mortality was accelerated under acidified conditions. Lastly, recovery rate of corals from bleaching was highest with lowest mortality rate in corals influenced by a single stressor. Recovery from bleaching was slowest and mortality highest in corals experiencing more than one climate change stressor.
