TOO MUCH STRESS FOR THE REEF?

The world's most comprehensive survey of coral bleaching has found that bleaching in the Great Barrier Reef Marine Park may be the worst on record.

The survey by scientists from the Australian Institute of Marine Science, CRC Reef and the Great Barrier Reef Marine Park Authority covered more than 640 reefs from the northern tip to the southern end of the Great Barrier Reef Marine Park using light aircraft. The team also used SCUBA to confirm results and determine whether corals were likely to recover from bleaching or would die.

Bleaching is a sign of stress. Corals appear bleached when they expel the tiny plants that usually live in their flesh. High water temperatures and other environmental conditions stress corals and can cause them to bleach. Many corals can recover from bleaching but if temperatures stay too high for too long, the corals will die.

"Our aerial surveys found that nearly 60% of the reef area in the marine park was heat-stressed to some extent as indicated by bleaching," said Dr Ray Berkelmans from CRC Reef who led the aerial survey team.

Not all reefs were bleached equally, and the bleaching was not evenly distributed throughout the Marine Park.

"Until now, the coral bleaching episode in 1998 was the worst on record, but the 2002 event was probably worse because more reef area was affected. The most severe bleaching occurred on reefs close to shore in both bleaching events, but the 2002 event has affected a greater area of reefs further offshore," said Dr Berkelmans.

The aerial surveys found that bleaching was worst in the Princess Charlotte Bay region, near the Turtle Island Group, on inshore reefs from Cape Upstart to the Whitsundays in some reefs in the Sir James Smith Group and in the Keppel Island area. Moderate to very high bleaching was seen inshore and offshore from around Cape Flattery to Mackay. Little or no bleaching was seen in the Far Northern Section from the tip of Cape York to the northern Princess Charlotte Bay area, in the Swains area and in the Capricorn Bunker Group.

"Our underwater surveys found that few reefs escaped bleaching, but it appears likely that most reefs will recover with only minor death of corals. However, we did find that some of the most severely bleached reefs were devastated with 50% and 90% of coral dead at some sites," said Dr Paul Marshall of GBRMPA who led the underwater surveys.

"Australia has been lucky to see another major bleaching event without widespread death of corals but the devastation we have seen at some sites provides a vivid warning of what could happen if hot water events become more frequent and severe. Although we can't control the weather, the GBRMPA is working to reduce other stresses to coral reefs," said Dr Marshall.

"We may be witnessing the beginning of a slow-motion degradation of the reef system that will only get worse in coming decades," said Dr Terry Done, from AIMS and CRC Reef. "AIMS, CRC Reef and the GBRMPA will continue to keep a careful watch on the health of the reef and improve our understanding of the implications of global warming for reef management."

Drs Berkelmans, Done and Marshall will hold a media conference at 10am on Thursday 23 May at CRC Reef, 6th floor, Northtown, 280 Flinders St, Townsville.

Download Bleaching Map Here - Full Colour - 490KB

Download Bleaching Map Here -Greyscale - 306KB

Photos available on request.

More information: Louise Goggin, Communication Coordinator, CRC Reef, on 07 4729 8404 or 0402 243116;Theresa Millard, Science Communication Manager, AIMS on 07 4753 4250 or 0409 596271; Barry Duncan,Communications Manager,GBRMPA, on 0408 722 064; Dr Ray Berkelmans (CRC Reef) on 07 4753 4268 or r.berkelmans@aims.gov.au; Dr Terry Done (AIMS/CRC Reef) on 07 4753 4344 or t.done@aims.gov.au