SYDNEY, Jan. 21 (UPI) -- Serious coral bleaching events are threatening Australia's Great Barrier Reef, scientists said Tuesday.
Coral bleaching is a stress condition that involves a breakdown of the symbiotic relationship between corals and zooxanthellae, a species of algae. The microscopic plants live within the coral tissue and provide food for growth and the coral's normal healthy color.
However, a rise in normal seawater temperatures of as little as 1 degree Celsius can cause the zooxanthellae to be expelled from the coral tissue, diminishing the color and sometimes leaving corals bone white.
Since 1980, scientists explained, there have been six worldwide bleaching events. Before then, they were unknown. In the most devastating event, in 1998, bleaching wiped out up to 90 per cent of coral in the Maldives, Sri Lanka, Kenya, Tanzania and the Seychelles.
"Right now, the alarm bell is ringing for the Barrier Reef," David Wachenfeld, a marine biologist with the government's Great Barrier Reef Marine Park Authority, told United Press International.
Ove Hoegh-Guldberg, director of the Center for Marine Studies at the University of Queensland, agreed.
"Bleaching is the No. 1 threat to coral reefs, and it is a major threat to the Barrier Reef," he told UPI.
If the water temperature cools, bleached corals can recover their symbiotic algae and return to their normal, healthy color. So far, for example, most of the Barrier Reef's corals have recovered from the 1998 and 2002 bleaching, which affected between 60 percent and 95 percent of the reef.
However, if temperature stress is too great or lasts several weeks or more, corals can die.
"We've been quite lucky," said Wachenfeld. "We've had widespread bleaching but restricted mortality. But the spatial extent and severity of bleaching is getting worse. Many scientists are concerned that as sea temperatures continue to rise the situation can only get worse."
Hoegh-Guldberg said the frequency of the bleaching events means corals might not have sufficient time to recover.
The bleaching particularly affects inshore and shallow water reefs and in Australia the biggest impact has been on staghorn, plate and fire corals.
"The corals won't disappear completely," Hoegh-Guldberg said. "They will bounce around, but many of the spectacular reef systems will disappear, and a great natural treasure will be lost."
The Great Barrier Reef Marine Park is the largest World Heritage site and is considered one of the wonders of the natural world due to its outstanding coral formations. The park hugs Queensland's eastern seaboard and stretches some 1,200 miles -- half the size of the state of Texas -- with 2,900 individual coral reefs representing almost 17 per cent of the planet's total.
As recently as last year, the Global Coral Reef Monitoring Network rated the Great Barrier Reef as having the healthiest coral in the world.
Pat Hutchings, president of the Australian Coral Reef Society, which represents coral reef researchers, told UPI her organization is urging actions to reduce greenhouse gas emissions, which many scientists suspect are responsible for global warming.
At present, the Australian government does not recognize global warming and is refusing to sign the Kyoto Protocol. Part of the reason, Hutching said, is the government's unwillingness to put a halt to Australia's record as the world's highest greenhouse gas producer per capita.
The Great Barrier Reef is one of Australia's most important tourist attractions, generating over $1 billion in tourism revenue each year.