Ocean Temperature Outlooks | Coral Bleaching Risk

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. Mass bleaching from thermal stress was also observed on Ningaloo Reef in 2011 and Scott Reef in 2016. 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 climate models such as ACCESS-S 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.

For satellite SST-based nowcasts for coral bleaching risk see ReefTemp Next Generation.