Coral cover along Australia's Great Barrier Reef has shrunk by half since 1985 as storms, warmer seas and starfish colonies kill off organisms, scientists said.
Coral covers almost 14 per cent of the 2,000-kilometre reef system, down from 28 per cent in 1985, researchers said in the Proceedings of the National Academy of Sciences. Forty-eight percent of the decline is a result of storms, 42 per cent is down to predatory starfish and 10 per cent to so-called bleaching caused by warmer waters, they said today.
"Coral cover could halve again by 2022," said Peter Doherty, a researcher at the Australian Institute of Marine Science in Townsville, Queensland, who helped create the monitoring programme.
The decline threatens the world's largest coral reef ecosystem, which hosts thousands of species of fish. The Global Coral Reef Monitoring Network said in 2008 that a fifth of the world's corals had already died and that many more would be lost by 2050 as carbon-dioxide emissions make waters more acidic and push global temperatures higher.
"This loss of over half of initial cover is of great concern, signifying habitat loss for the tens of thousands of species associated with tropical coral reefs," the researchers wrote. "The rate of decline has also increased substantially and has averaged about 1.45 per cent per year since 2006."
While scientists could not stop storms, the reefs could be protected by improving water quality to stem the spread of the crown-of-thorns starfish, they said. Nutrient-rich agricultural run-off helps the starfish's larvae survive. Without the starfish, coral cover would expand by 0.89 per cent a year, as opposed to the 0.53 per cent shrinkage it had averaged since 1985, the researchers said.