Changes in atmospheric greenhouse gas concentrations have brought two changes to oceanic ecosystems – ocean warming and ocean acidification (Kleypas et al., 1999). Ocean water warming is a well-recognised phenomenon (Hoegh-Guldberg, 1999), and recent evidence also indicates that ocean acidification has already commenced at tropical coral reefs, such as the Great Barrier Reef (Wei et al., 2009, Uthicke et al., 2014). Ocean warming threatens coral reefs through driving the occurrence of coral bleaching, whilst ocean acidification decreases the growth rate and skeletal quality of marine calcifying animals and plants (Hoegh-Guldberg et al., 2007). Evidence has emerged that ocean acidification may also impact the symbiotic relationship between corals and dinoflagellate algae, and may potentially impact the phenomenon of coral bleaching (Anthony et al., 2008). Where several environmental parameters change at once, it is important to understand the response of corals not only to change in each factor in isolation, but to changes in all factors simultaneously, to identify synergistic effects (Coles and Jokiel, 1978).