While the World Heritage-protected site, which sprawls for more than 345,000 square km off Australia’s east coast, is in a better position than most other reefs globally, the risk of its destruction was mounting.

"Even with the recent management initiatives to improve resilience, the overall outlook for the Great Barrier Reef is poor and catastrophic damage to the ecosystem may not be averted," a government reef management body said. The five-yearly reef Outlook report, aimed at benchmarking the health of the reef, found climate change, declining water quality from coastal runoff, development and illegal fishing were the biggest dangers to the reef. The study echoed findings by scientists belonging to the UN Intergovernmental Panel on Climate Change that the Great Barrier Reef could be "functionally extinct" within decades, with deadly coral bleaching likely to be an annual occurrence by 2030.

The reef was one of the most diverse and remarkable ecosystems in the world, and populations of almost all marine species were still large, the government’s Great Barrier Reef Marine Park Authority said in the report.

But some ecologically important species, such as dugongs, marine turtles, seabirds, black teatfish and some sharks had declined significantly, while coral diseases and pest outbreaks like crown-of-thorns starfish appeared to be increasing and becoming more serious.

A separate report by the Australian Institute of Marine Science, found ocean temperatures on northern parts of the reef had been a degree above average through winter, pointing to a bad year for coral bleaching.

"We know that a failure to act on dangerous climate change puts at risk significant places like the Great Barrier Reef and this report confirms the scale of the challenge ahead," Austr-alia’s environment minister Peter Garrett said. Bleac-hing occurs when the tiny plant-like coral organisms die, often because of higher temperatures, and leave behind only a white limestone reef skeleton.

—Reuters