Coral Bleaching in the Great Barrier Reef
Bleached Staghorn corals
Image courtesy of GBRMPA (Commonwealth of Australia)
Elevated sea temperatures are the primary cause of mass coral bleaching events. Bleaching is a stress response of corals, during which they expel their zooxanthellae during unfavourable conditions, giving rise to the typical white colouration observed. Aside from temperature, other stressors such as tropical cyclones, freshwater inflows and anthropogenic pollution can also induce bleaching but to a far lesser extent and generally not on large spatial scales.
Bleaching has been observed on the Great Barrier Reef since 1982, with severe bleaching events occurring in the summers of 1998, 2002 and 2006. Major bleaching events in Southern Hemisphere reefs (Pacific and Indian Oceans) tend to occur in February-April, with a lag of up to a month in the bleaching response of corals following thermal stress. Mortality appears to increase with the intensity of the bleaching event, which is determined by how much and for how long temperatures remain above the maximum mean summer temperatures.
Seasonal forecasts from coupled dynamical models such as POAMA can be used to detect sea surface temperature anomalies (SSTA) several months in advance, allowing for proactive management responses. These products have revolutionised the way in which coral bleaching events are monitored and assessed in the Great Barrier Reef and Coral Sea.
For more information on coral bleaching refer to the Great Barrier Reef Marine Park Authority.