Great Barrier Reef coral bleaching worst on record: Aussie scientist

Bleaching to Australia's Great Barrier Reef (GBR) is the worst on record with 95 percent of the northern reaches ranked in the two most severe categories.

Human induced climate change has been increasing the frequency of mass coral bleaching events, further strengthened by the El Nino re-enforced warm water travelling through the equatorial pacific, causing mass bleaching events in Fiji, New Caledonia and Kiribati, among others.

Convenor of the National Coral Bleaching Taskforce, James Cook university professor of coral reef studies Terry Hughes told local media on Tuesday only four of the 550 reefs surveyed between Cairns and Papua New Guinea in the world heritage listed marine park appeared to be untouched from the mass bleaching event.

"The north has fried," Hughes said.

"The severity is much greater than in earlier bleaching events in 2002 or 1998."

The northern section of the GBR is the most pristine of the reef system, widely used by the Australian authorities to argue against the reef being listed as "in danger" by UNESCO. Australia is due to report back to UNESCO on its reef management by the end of 2016 to remain off the "in danger" list.

"Even more concerning, we haven't yet found the southern limit of the bleaching," Hughes said, adding further surveys between Cairns and Townsville will be central to identify where it stops.

"Thankfully, the southern Reef has dodged a bullet due to cloudy weather that cooled the water temperatures down."

Australian scientists have stepped up surveying the reef system after bleaching was first noticed in February. They're reporting a 50 percent mortality rate of bleached corals, "but it's still too early to tell just what the overall outcome will be," Hughes said.

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

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.

Recent research suggests corals with high levels of fat or other energy reserves can withstand annual bleaching events, which is critical to predicting the persistence of corals and their capacity to recover from more frequent events resulting from climate change.

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 2000 kilometers along Australia's northeastern coastline, bringing in billions of dollars in tourism revenue each year. Endit