The plight of coral reefs

"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. Could you imagine if a single event wiped out 16% of the Amazon forest, or 16% of ecosystems in the UK? Not only will ecology be affected, economy will be too.
"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. 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.

Adding to this, scientists have come to realise in recent years, is ocean acidification. The water absorbs some of the atmosphere's extra carbon dioxide, making it slightly more acid, enough to compromise the capacity of corals to build their skeletons, and snails to build their shells.

Overfishing in many regions - especially the use of dynamite to fish in East Asia and heavy trawls that reduce reefs to rubble - the excavation of building materials from reefs, coastal development, invasive species and pollution are all fingered in the new analysis.

The political response to climate change, said Alex Rogers, could be likened to "fiddling while Rome burns".

"I don't think politicians and the public are aware of the gravity of the situation we're in regarding coral reefs and other marine ecosystems." About one quarter of marine species are believed to depend on coral at some stage of their development. Many fish live their entire lives on reefs, while others use them as nurseries; presumably if the coral dies out, so do the fish. The economic impact of losing coral is also significant.

References: http://news.bbc.co.uk/2/hi/science/nature/7498502.stm