Research > Coral Bleaching

Coral bleaching occurs when the symbiosis between reef-building corals and their symbionts (zooxanthellae) breaks down, releasing the brown algal symbionts and turning the a brilliant white colour (hence bleaching). Bleaching can be triggered by a number of stresses including extremes of heat, light and salinity; toxins such as cyanide (used in poison fishing) and herbicides. Bleaching occurs in all invertebrates that harbour symbiotic algae. 

Coral bleaching: The harbinger of rapid climate change?

Although the first observations of coral bleaching date back to over 100 years ago, observations of the mass bleaching of entire reefs and regions was not reported in the scientific literature until the early 1980s. During mass bleaching events most of the corals in a community or Reef undergo bleaching. These events have been tracked down to periods in which sea temperatures rise a few degrees above the long-term summer maxima for short periods. These events subsequently have been related to the anthropogenic warming of the world's oceans as result of global warming. This has provoked the spectre of mass coral bleaching becoming more frequent and intense as oceans warm.

Understanding coral bleaching from physiology to ecology

Our research group has been at the forefront of studies of the physiology and ecology of mass coral bleaching. Early studies focused on exploring the link between elevated temperatures and the physiology of symbiosis, leading to the photoinhibition hypothesis for explaining mass coral bleaching. Other studies investigated how changes in sea temperature in the field coincided with mass coral bleaching events. More recent studies have focused on relating the physiology of coral bleaching and mortality to how sea temperatures might vary in the future.

Key questions

1. How does mass coral bleaching and mortality varied between different types of Symbiodinium and coral species?

2. What are the cellular processes (e.g. apoptosis, necrosis) involved in coral bleaching and how do they relate to the release of Symbiodinium to the environment.

3. What are the physiological changes that trigger coral bleaching and how are they affected by other stresses such as ocean acidification, elevated light, turbidity and pollution?

4. What are the consequences of coral communities that are decimated by heat stress on the biological diversity and ecological structure of tropical shell communities?

Hoegh-Guldberg O, Smith GJ (1989) The effect of sudden changes in temperature, light and salinity on the population-density and export of zooxanthellae from the reef corals Stylophora pistillata and Seriatopora hystrix. J Exp Mar Biol Ecol 129:279-303

Hoegh-Guldberg O (1999) Climate change, coral bleaching and the future of the world's coral reefs. Mar Freshw Res 50:839-866

Hoegh-Guldberg O (1999) Climate change, coral bleaching and the future of the world's coral reefs. Mar Freshw Res 50:839-866

Fitt WK, Gates RD, Hoegh-Guldberg O, Bythell JC, Jatkar A, Grottoli AG, Gomez M, Fisher P, Lajuenesse TC, Pantos O, Iglesias-Prieto R, Franklin DJ, Rodrigues LJ, Torregiani JM, van Woesik R, Lesser MP (2009) Response of two species of Indo-Pacific corals, Porites cylindrica and Stylophora pistillata, to short-term thermal stress: The host does matter in determining the tolerance of corals to bleaching. Journal of Experimental Marine Biology and Ecology 373:102-110