Killer starfish threaten Great Barrier Reef

Crown-of-thorns starfish have a voracious appetite and waves of carnivorous starfish are eating their way through Australia's Great Barrier Reef - and sugar cane farming is being blamed.

Researchers at Australia's Institute of Marine Science (AIMS), just outside Townsville, Queensland, in north-east Australia, have mapped the pattern of destruction.

"Coral cover is half of what it was 27 years ago, coral cover is going down at an alarming rate." Dr Katharina Fabricius, coral reef ecologist and AIMS principal research scientist, told the BBC World Service programme Discovery.

She said the biggest culprit was the Crown of Thorns Starfish (COTs).

"There are three main sources for the coral decline, one is storms, however 42% is attributed to Crown of Thorns Starfish - and just 10% due to bleaching. This compares with 70% due to bleaching for reefs elsewhere in the world , such as in the Caribbean."

“Crown of Thorns are very fecund animals - each female can produce between five and 20 million eggs ”
John Brodie, James Cook University

Bleaching occurs when corals are stressed by changes in conditions such as temperature, light, or nutrients. They expel the symbiotic algae living in their tissues, causing them to turn completely white.

Australian scientists are now looking at ways to reduce the destruction wreaked by starfish, which have the ability to smother coral and digest the fleshy parts.