Coral Bleaching

These pages provide information on sea surface temperatures for monitoring coral bleaching events in the Great Barrier Reef, Australia. See latest on the 2016 and 2017 marine heatwave on the reef.

Coral Bleaching in the Great Barrier Reef

Bleached coral image Bleached Staghorn corals

Image courtesy of the Great Barrier Reef Marine Park Authority (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, 2006, and more recently 2016/2017. Major bleaching events in Southern Hemisphere reefs (Pacific and Indian Oceans) tend to occur in February to 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 ACCESS-S1 can be used to detect anomalous SSTs 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.

Further reading

  • Baker A.C., Glynn P.W. and Riegl B., 2008: Climate change and coral reef bleaching: An ecological assessment of long-term impacts, recovery trends and future outlook. Estuar. Coast. Shelf Sci. 80, 435–471.
  • Hoegh-Guldberg O., 1999: Coral bleaching, climate change and the future of the world's coral reefs. Review. Mar. Freshw. Res., 50, 839–866.
  • Maynard J.A., Johnson J.E., Marshall P.A., Eakin C.M., Goby G., Schuttenberg H., Spillman C.M., 2009: A strategic framework for responding to coral bleaching events in a changing climate. J. Env. Manage., 44, 1–11.
  • Spillman C.M., 2011: Operational real-time seasonal forecasts for coral reef management. J. Oper. Oceanog., 4, 13–22.
  • Spillman C.M. and Alves O., 2009: Dynamical seasonal prediction of summer sea surface temperatures in the Great Barrier Reef. Coral Reefs, 28, 197–206.
  • Spillman C.M., Alves O., Hudson D.A., 2011: Seasonal prediction of thermal stress accumulation for coral bleaching in the tropical oceans. Mon. Weather Rev., 139, 317–331