A bout of coral bleaching hitting Australia's Great Barrier Reef could be as bad as an episode in 2001-2002 that affected 60 percent of the reef, scientists warned Tuesday.
An international team studying the world's reefs said in a statement that water temperatures for the past four months off Australia's northeastern coast have been well above long-term averages.
He said temperature measurements were similar to those in 2001-2002, which led to the worst coral bleaching ever recorded on the Great Barrier Reef.
"In that event, over 60 percent of the Great Barrier Reef bleached and up to five percent of reefs suffered serious damage," he added.
Hoegh-Guldberg chairs the Bleaching Working Group for the Coral Reef Targeted Research and Capacity Building for Management Program, a worldwide network of more than 100 scientists.
Coral bleaching occurs when the microscopic plants, or zooxanthellae, which live in coral tissue stop working due to stress that often is caused by rising temperatures. The zooxanthellae provide corals with color and food.
Coral reefs are not immediately killed by bleaching and if they are not severely stressed, they can recover their zooxanthellae and regain their color.
Bleaching already has whitened coral around the Keppel islands at the southern end of the Great Barrier Reef, a World Heritage-listed chain of reefs that stretches for almost 1,200 miles along most of the coast of Australia's Queensland state.
"Corals at the Keppels are completely bleached and we are only halfway through January," Hoegh-Guldberg said. "How this will develop across the Great Barrier Reef is the number one question right now."
Healthy coral is key to marine ecosystems along the reef and also to a multibillion dollar tourist industry in Australia, where the Great Barrier Reef is one of the top draws.
Paul Marshall, manager of the Great Barrier Reef Marine Park Authority's Climate Change Response Program, said that while most of the tourism is based around the northern stretches of the reef, there are reefs of ecological importance and several popular resorts around the southern reaches.
Marshall said there had been reports late last year of some bleaching in the north of the reef, but temperatures there had since dropped while in the south temperatures continued to be above average.
"We are going to be pretty lucky to escape coral deaths in the southern Great Barrier Reef," he said.
"It's going to have to be some pretty serious cloudy conditions to avert more serious bleaching down there," he added.