Great Barrier Reef Coral Bleaching part of a Hemispheric Event

The late summer to autumn bleaching of corals currently being observed on parts of the Great Barrier Reef is part of a very widespread phenomenon. ‘Reports of bleaching so far this year have been coming in through the internet from places as far apart as Mauritius off east Africa, the Red Sea, to Samoa and the Galapagos Islands in the Pacific Ocean’ says Dr Terry Done, Principal Research Scientist at the Australian Institute of Marine Science. ‘Two teams from AIMS have just returned from surveys of sections of the Great Barrier Reef. They reported that bleaching is virtually absent across the entire width of the Great Barrier Reef around the Whitsunday Islands, and on the outer reefs north of Cairns, so the main tourism destinations have been spared. However some of the reefs they visited off Townsville have so much bleached coral they looked like they were covered in snow drifts’.

Coral bleaching is caused by the loss of pigments and microscopic plant cells from the coral tissues that results in the whitening of the coral. It is caused by a variety of stresses to the coral, including changes in seawater temperature, salinity, and light. There are worldwide concerns that apparent increases in bleaching are linked with global climate change, high temperatures and El Niño.

Survey leader Dr Lyndon DeVantier said ‘The most intense effects we saw occurred on a nearshore reef AIMS has been monitoring since 1980. Bleaching had occurred to the base of the reef slopes, with substantial and continuing death of corals, particularly on the shallow reef tops. Around the time of the Townsville floods, the corals were exposed to a minor temperature fall and a major fall in salinity to around 20 parts per thousand. Over the next month, that stress was compounded by a huge increase in sea temperature to 32 degrees.’

The scientists believe that it was the combination of the two stresses that triggered the bleaching. ‘We've been following the fate of a huge boulder coral we call Friar Tuck for many years’ says Devantier. ‘The Friar would have been about 500 years old when Captain Cook sailed past just 227 years ago. It is presently completely white, and its fate now depends on the weather conditions of the next few months.’

Cruise leader Emre Turak obtained extensive photographic and video records of the bleaching. ‘On reefs further offshore, most intense bleaching has occurred on the shallow reef tops, where most corals are white or ‘fluorescent’ pinks and blues. Although very appealing, these colours indicate that the corals are feeling very stressed. Below about 6 m depth, there was a substantial decline in bleaching’ said Turak.

Done is still unsure of the ecological impact or consequences of the current bleaching. ‘It is clear that weather conditions over the next few months will be crucial. A key to the severity and uniqueness of the present event lies inside the very large boulder corals like Friar Tuck. The death of Friar Tuck and other ancient corals would indicate that the weather of this past summer has been unprecedented in the lives of these corals, the Redwoods of the reef’. The team brought back some coral specimens for analysis. ‘Analysis of records in their skeletons can aid in our understanding of the causes of this event’ said DeVantier. ‘Continued research and monitoring should unlock some of the answers, presently sealed in stone’.

For further information contact:
Dr. Terry Done, AIMS - ph: +61 (07) 47534344, fax: +61 (07) 47725852
Dr Lyndon DeVantier - AIMS, ph (07) 47534399, fax (07) 47725852
Wendy Ellery - AIMS, (07) 47534409, fax (07) 47716138