Alarming' plight of coral reefs
By Richard Black
Environment correspondent, BBC News website
Warming waters, a consequence of climate change, can devastate coral
A third of the world's reef-building coral species are facing extinction.
That is the stark conclusion from the first global study to assess the extinction risks of corals.
Writing in the journal Science, researchers say climate change, coastal development, overfishing, and pollution are the major threats.
The economic value of the world's reefs has been estimated at over $30bn (£15bn) per year, through tourism, fisheries and coastal protection.
"The picture is frightening," said Alex Rogers from the Zoological Society of London, one of 39 scientists involved in the assessment.
Could you imagine if a single event wiped out 16% of the Amazon forest, or 16% of ecosystems in the UK?
Alex Rogers, ZSL
"It's not just the fact that something like a third of all reef-forming corals are threatened, but that we could be facing the loss of large areas of these ecosystems within 50 to 100 years.
"The implications of that are absolutely staggering - not only for biodiversity, but also for economics."
The analysis shows that reef-building corals are more threatened than any group of land-dwelling animals except amphibians.
The most dramatic decline in recent years was caused by the 1997/8 El Nino event, which caused waters to warm across large swathes of the tropics.
CORAL - KEY FINDINGS
Known species of reef-building coral: 845
Enough data to assess 704
Critically endangered: 5
Near threatened: 176
Least concern: 297
The Red List definitions
When water temperatures rise, coral polyps - tiny animals that build the reefs - expel the algae that usually live with them in a symbiotic relationship.
The corals lose their colour, with reefs taking on a bleached appearance, and begin to die off because the algae are not there to provide nutrients.
The new analysis shows that before 1998, only 13 of the 704 coral species assessed would have been classified as threatened. Now, the number is 231.
"It was a devastating event in terms of the destruction of corals, with 16% of reefs irreversibly destroyed - an incredible amount," said Kent Carpenter from Old Dominion University in Norfolk, Virginia, in the US.
"The big problem is that if these bleaching events become more frequent as temperatures rise, as we suspect will happen, then we will see whole tracts of coral wiped out."