Scientists are concerned that rising temperatures could produce a coral bleaching episode reminiscent of the 1998 crisis if relief from current temperatures does not occur. These concerns are being addressed this week by an elite international group of experts at a workshop on Magnetic Island, Queensland.

Currently, a research program undertaken by AIMS, GBRMPA and NOAA is using thermal satellite imaging to identify hot spots on the reef.

The program recently revealed higher than normal conditions on the reef with water temperatures exceeding 30 degrees C. These unusually high temperatures have raised concerns that corals may bleach in large numbers this summer. AIMS researcher Dr Terry Done and a team of CRC researchers have surveyed five reefs in the Townsville sector of the Great Barrier Reef at distances from five to 130km off the coast.

Reef slopes off Myrmidon reef, where AIMS maintains a GBR weather station, were healthy and normal in colour. Corals living on reef-tops, however, were bleached but otherwise healthy. At Magnetic Island, the reefs revealed bleached, diseased and dying corals amongst the silty shallow waters on Townsville’s doorstep.

"A few more weeks of exposure to the prolonged hot and calm weather could cause severe bleaching," Dr Done said last Friday (Jan.25).

High water temperature is the most prevalent stress leading to coral bleaching. Bleaching occurs when corals encounter stressful environmental conditions.

Stresses cause coral to expel zooxanthellae, the small algae living inside the bodies of coral. Because the zooanthellae give the coral their colour, when they dissipate the corals suffer a loss of colour, hampering the photosynthesis process. This eventually leads to their death.

Damage was patchy but severe in some areas. North of Townsville, in the Palm Island group, some reefs were devastated with up to 80% of corals dying within months. Scientists are fearing a similar situation this year if weather conditions do not change.

In January a pool of hot water began to scorch corals and scientists are worried warm temperatures could cause serious irreparable damage to the GBR if this pool returns.

Dr Done suggests a period of cloudy and cooler weather is needed to counteract the current hot conditions we’ve been having.

Water temperatures throughout the GBR have cooled slightly in the last week of January, but are still about half a degree above average for this time of year.

On average, between December and April each year, the Eastern Australian coast is visited by two or three cyclones. This year residents along the east coast are yet to see a cyclone.

Corals are able to recover from bleaching in a period of weeks to months providing they are only slightly stressed. But if they die in large numbers, it takes a period of several years before new corals emerge, taking over spaces left by dead corals. Changes in our climate, due to human impacts such as greenhouse gas emissions cause overall increases in temperatures and hamper recovery from natural phenomena such as coral bleaching.

With global temperatures predicted to rise up to 2.4 degrees C in the 21 century, a sense of urgency now exists to better manage and protect the health of our coral reefs.

Dr Skirving, a satellite oceanographer, stresses the importance of collecting the correct data required to keep track of bleaching and predict which reefs will be vulnerable.

Indeed, if scientists, oceanographers, reef managers and world aid organisations continue to collaborate and share resources, the best information about our delicate reefs can be brought to the world.

"At our meeting, we are seeking to all reach the same understanding of the issues. This is important, if scientists are to respond quickly and effectively as events occur, and for managers and policy makes to make plans on how best to deal with the future," said Dr Skirving.

For more information, 
Stay tuned to the AIMS website for the rest of the coral bleaching story, as Summer 2002 progresses …