Corals join frogs and toads as world's most endangered

From an article by Catherine Brahic in the New Scientist:

Within one generation, diving on coral reefs could be a very rare holiday opportunity. The first comprehensive review of tropical coral species reveals that over one-quarter reef-building coral species already face extinction.

This means corals join frogs and toads as the most threatened group of animal species on the planet.

There are 845 known species of corals that build reefs and live in symbiosis with algae. Not enough is known about 141 of these to determine how threatened they are. But of the 704 remaining species, scientists say 32.8% are at risk of extinction.

The team, which was led by Kent Carpenter of the International Union for the Conservation of Nature (IUCN) and gathered experts from around the world, used the IUCN Red List criteria to assess the 845 species.

Sewage and climate

Two hundred and thirty one species (27%) were found to be threatened with extinction. A further 176 (21%) were deemed "near-threatened".

"It was a huge surprise because there is only one other group of animals that has been assessed that exceed that level of threat," says Alex Rogers of the Zoological Society of London, who participated in the survey, "and that's the amphibians."

Humans directly threaten corals by dumping fertilisers and sewage into the oceans and by overfishing with destructive methods.

All this encourages the growth of larger algae, which smother corals. "Outside of the US and Europe, 80% of human sewage is released into the oceans without treatment," says Rogers.

Global warming increases sea temperatures which causes "bleaching" events, where the reefs expel the tiny algae upon which they depend. Warming has also been associated with an increased incidence of coral diseases.