Environmental News Service, May 23, 2002
TOWNSVILLE, Queensland, Australia, May 23, 2002 (ENS) - Coral bleaching in the Great Barrier Reef Marine Park may be the worst on record, scientists said today after the most comprehensive aerial survey ever conducted. The survey is aimed at helping unravel the implications of global warming for reef management.
"Our aerial surveys found that nearly 60 percent 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. Coral bleaching is the loss of color from corals that can lead to their death.
"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," said Dr. Berkelmans.
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.
Coral bleaching is a response to stressful environmental conditions in corals, says Dr. Terry Done of the Australian Institute of Marine Science and CRC Reef. It is caused when the small algae that live inside the bodies of most corals - their zooxanthellae - leave the corals. Some corals can recover from bleaching by regaining their zooxanthellae, but others may die.
Not all reefs in the Great Barrier Reef Marine Park were bleached equally, and the bleaching was not evenly distributed throughout the park, the aerial surveys found. Generally, the most severely bleached areas were in the southern part of the park, while the northern sections were less 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, said Dr. Paul Marshall of the Great Barrier Reef Marine Park Authority (GBRMPA) who led the underwater surveys.
"We did find that some of the most severely bleached reefs were devastated with 50 percent and 90 percent of coral dead at some sites," he said.
"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. Done.
Reefs can recover from coral bleaching, the scientists say. If a reef is only briefly and slightly stressed, only a few scattered corals will die. That reef can recover within a few years as new corals arrive and settle in the empty spaces vacated by the dead corals.
But, says Dr. Done, if a majority of the corals die in a severe bleaching event, including very large, old corals, complete recovery would take as long as the age of the oldest coral. It could take hundreds of years until the coral community has a similar age structure to that before the event.
Recovery will be hampered, the scientists say, if the reef is in a location that has high levels of dissolved or organic nutrients and low numbers of grazing fishes, sea urchins and snails. This combination allows some seaweeds to establish which form a carpet that is impenetrable to coral larvae and delays the commencement of recovery by corals.
A change in the climate so that the reef is repeatedly exposed to high temperatures on an annual basis will also hamper recovery.
CRC Reef is the Cooperative Research Centre for the Great Barrier Reef World Heritage Area incorporated as CRC Reef Research Centre Ltd. Scientists from this center together with the Australian Institute of Marine Science said they will keep a careful watch on the health of the corals and improve their understanding of how global warming impacts the world's longest reef.
Great Barrier Reef suffers heat damage
Researchers in Australia claim that sea temperatures around the Great Barrier Reef are now so high that major damage has been caused to the world's biggest marine park.
The principal danger to the reef, according to scientists, is the bleaching of coral caused by unusually warm water.
The Australian Institute of Marine Science says that 2002 has been the hottest year on record for the reef, which stretches 2,000 kilometres (1243 miles) along Australia's east coast.
It has drawn up a heat map that has plotted the change in sea temperatures around the reef over the past 10 years.
The results are causing researchers concern.
They have discovered that significant bleaching of the reef has occurred, causing the coral to lose its energy-giving algae, turn white, and in some cases, die. The map has allowed scientists to see where the problem areas are.
Warm weather is considered to be a factor, but the reasons are complex. The exact cause of bleaching is not known.
Solar radiation, extreme low tides, and reduced salinities are also believed to be additional triggers. What is known is that excessive whitening of the coral can cause the reef to crumble.
Protecting the reef
The Australian Institute of Marine Science was established by the federal government 30 years ago to help protect aquatic environments around the country's vast coastline.
The institute also reports on the impact of humans on the Great Barrier Reef and those of natural disturbances, such as outbreaks of Crown of Thorn starfish and cyclones.
Coral is classified as an animal and is related to sea anemones and jelly-fish.
Reefs are made up of layers of coral skeletons cemented together by algae to form an extremely hard limestone structure.
The Great Barrier Reef is a complex of almost 3,000 separate reefs and is one of Australia's principal tourist destinations.
Last year the Australian Senate passed new laws in an effort to protect the area from negligent mariners and oil-spills following a series of shipping disasters.