Soaring ocean temperatures in the Caribbean have caused the first mass die-off of coral in the region for 3,000 years.

Scientists suspect that the record temperature of 31.5 deg Celsius, recorded in 1998 off Belize, was the result of global warming and the El Nino climate phenomenon.

The raised heat level lasted for several months and caused virtually all the Belize coral colonies to bleach and die.

Serious coral bleaching has been previously reported in both the Pacific and Indian oceans, but this is the first such occurrence in the Caribbean.

Loss of colour

"There is growing concern that global climate change is degrading coral reef ecosystems, with coral mortality increasing as a result of bleaching and emergent diseases: our results from Belize appear to justify this concern," said Richard Aronson of the Dauphin Island Sea Laboratory in Alabama, US.

The Belize barrier reef is the largest in the Northern Hemisphere.

Scientists believe high temperatures cause the little organisms that live in coral reefs to expel the microscopic algae that share their home. This weakens the colony and further stress leads to the death of the reef.

The loss of the algae also robs the reef of its colour, which is why it is called bleaching.

Australia's Great Barrier Reef has experienced bleaching for the past 20 years and severe bleaching occurred there in 1998.

Coral history

But Dr Aronson and his colleagues said there was no record of mass bleaching along the Belizean barrier reef before an episode in 1995 when most coral colonies recovered.

But in 1998 sea temperatures in the central section of the reef, which rarely exceed 29 deg C were greater than 30 deg C for months.

Surveys done in 1999 and 2000 showed the most abundant coral on the reef, Agaricia tenuifolia, was killed and other species were also damaged.

The researchers then used radiocarbon dating on 12 coral cores to determine historical events on the reefs. This showed no similar bleaching had happened for more than 3,000 years.

The research is published in the journal Nature.