Over the past 27 years, Australia’s Great Barrier Reef has lost half of its coral, mainly due to storm damage and predatory starfish, according to a new study.

The Great Barrier Reef is actually a system of more than 3,000 coral reefs that spans more than 116,000 square miles. It plays host to a wide range of wildlife, from fish to turtles to dolphins and dugongs.

Thanks to its distance from human habitats and strong legal protections enacted by Australia, the Great Barrier Reef is one of the least-threatened coral reefs in the world. But it is not invulnerable.

Researchers from the Australian Institute of Marine Science and the University of Wollongong say in a paper published in the Proceedings of the National Academy of Sciences that nearly half of the damage to the reef is from powerful storms, while 42 percent of the damage can be attributed to the voracious crown of thorns starfish. Ten percent of the damage is due to bleaching, which is a side effect from ocean warming, according to the paper.

The team’s results are based on 2,258 reef surveys conducted by AIMS at 214 different reefs within the Great Barrier Reef over the last 27 years.

“Our data show that the reefs can regain their coral cover after such disturbances, but recovery takes 10 to 20 years,” AIMS researcher Hugh Sweatman said in a statement Monday. “At present, the intervals between the disturbances are generally too short for full recovery, and that’s causing the long-term losses.”

If nothing is done to combat the losses, the authors estimate that the reef will lose 50 percent of its present coral coverage by 2022.

“We can’t stop the storms and ocean warming“ -- the primary cause of coral bleaching -- which “is one of the critical impacts of the global climate change,” AIMS CEO John Gunn said in a statement. ”However, we can act to reduce the impact of crown of thorns,” he says.

In the absence of the starfish, coral cover would increase by .89 percent each year, even factoring in losses due to storms and bleaching, according to the study.

While it’s doubtful that conservationists will want to completely eliminate the crown of thorns starfish, there may be ways to control population explosions that can wreak havoc among the coral beds. There needs to be more research on how to target the starfish larvae in high-risk regions of the coral reef, the authors said.

Improving water quality may be a way to control starfish population spikes, according to the paper.

And looking toward the long-term, “mitigation of global warming and ocean acidification is essential for the future" of the Great Barrier Reef, the authors said.

SOURCE: De’ath et al. “The 27-year decline of coral cover on the Great Barrier Reef and its causes.” PNAS published online 1 October 2012.

Australia