Scientists have for the first time documented the killing of a coral reef in the Caribbean by global warming. They warn that it could herald a widerdestruction of the world's coral population.
The central barrier reef off Belize has suffered a mass die-off since scientists recorded the highest sea temperatures there in 1998, which resulted in widespread coral "bleaching". Richard Aronson, a marine biologist at the Dauphin Island Sea Lab in Alabama, working with colleagues at the Smithsonian Institution in Washington DC, describes in the journal Nature the first complete collapse of a coral reef in the Caribbean from bleaching.
The lettuce coral was the most abundant coral species living on the central Belizean lagoon in 1998, yet surveys in subsequent years showed that virtually all living colonies had been bleached white at almost every depth investigated.
Cores drilled into the coral showed a similar bleaching had not taken place in the past 3,000 years, indicating that the mass killing was unprecedented in recent history. Dr Aronson said: "1998 was the hottest year on record in the tropical oceans of the world. The high temperatures were created by a combination of El NiÃ±o conditions and continuing global warming. This caused coral bleaching worldwide.
"In Belize, coral populations in lagoonal habitats were killed by the bleaching, and this is the first time that anyone has observed a mass coral kill related to bleaching in the Caribbean."
Extensive coral bleaching has already been recorded elsewhere in the Pacific and Indian oceans. Marine biologists believe high temperatures cause a breakdown of the relationships between the coral animal - a sea anemone-like creature - and the microscopic algae that live in its chalky "skeleton". When sea temperatures reach 30C, the coral expels about 90 per cent of the algae, causing the colony to lose its colour. The reef can recover but is weakened and a second bleaching episode can kill it.
Dr Aronson said: "In the Belizean lagoon in 1998, the high water temperatures lasted for many months, causing the corals to bleach and then die. They were too stressed by the high temperatures to survive and regain their algae."
The case of the lost Belizean coral justifies the growing concern about global coral degradation caused by the Earth's ever-warmer climate, Dr Aronson said.