Coral death toll rises on Australia's Great Barrier Reef

Mass bleaching has killed 35 percent of corals on sections of the Great Barrier Reef between Papua New Guinea and Townsville, coral reef scientists said on Monday.

Researchers from the ARC Centre of Excellence for Coral Reef Studies noted however that some parts of the reef were in much better shape.

"Some reefs are in much better shape, especially from Cairns southwards, where the average mortality is estimated at only 5 percent," ARC Centre Director Professor Terry Hughes said.

"This year is the third time in 18 years that the Great Barrier Reef has experienced mass bleaching due to global warming, and the current event is much more extreme than we've measured before."

Coral bleaching occurs when stress such as heat caused the animal to expel the symbiotic algae, loosing vital nutrients and energy reserves, thus color, leading to the wide scale loss of productive habitats for fish.

The coral host then becomes weak and susceptible to disease. When bleaching is prolonged, the animal can die.

"These three events have all occurred while global temperatures have risen by just 1 degree Celsius above the pre-industrial period," Hughes said.

"We're rapidly running out of time to reduce greenhouse gas emissions."

Coral reefs are one of the most important and productive marine ecosystems that the world depends on for tourism and fisheries sustainability.

Severe bleaching events, however, may take highly impacted coral reefs up to 10 years to recover.

The Great Barrier Reef, the world's largest living ecosystem, spans some 2,000 km along Australia's northeastern coastline, bringing in billions of dollars in tourism revenue each year. Endit