Half of Great Barrier Reef 'disappeared' in past 27 years
2 October 2012 Last updated at 07:07 BST
More than half of Australia's Great Barrier Reef has disappeared in the past 27 years, according to a new study by scientists.
Various factors, including cyclones, coral bleaching and the Crown of Thorns starfish, have been blamed.
The BBC's Duncan Kennedy reports from Sydney.