Various factors, from cyclones to the Crown of Thorns starfish,

are being blamed for the loss of the reef.

Australia's Great Barrier Reef has lost more than half its coral cover in the past 27 years, a new study shows.

Researchers analysed data on the condition of 217 individual reefs that make

up the World Heritage Site.

The results show that coral cover declined from 28.0% to 13.8% between 1985

and 2012.

They attribute the decline to storms, a coral-feeding starfish and bleaching

linked to climate change.

The research is published in the Proceedings of the National Academy of

Sciences journal.

Glen De'ath from the Australian Institute of Marine Science (AIMS) and

colleagues determined that tropical cyclones - 34 in total since 1985 - were

responsible for 48% of the damage, while outbreaks of the coral-feeding

crown-of-thorns starfish accounted for 42%.

Two severe coral bleaching events in 1998 and 2002 due to ocean warming also

had "major detrimental impacts" on the central and northern parts of the reef,

the study found, putting the impact at 10%.

"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