Reefs: Coral's Faltering Partnership; The 'rainforests of the seas' may need to be saved, too.(Cover story)

Byline: Mac Margolis (With Fernando De Freitas in Darwin and Karla Bruning in New York)

With their rainbow hues and the splendid variety of species they cater to, coral reefs are often called the rainforests of the seas. They might also be described as the ocean's architects--a consortium of tiny polyps hurling up high-rises of calcium-carbonate, which they mine from the seawater. Covering just 1 percent of the Earth's surface, they may host 25 percent of all marine life, which makes the reefs true underwater metropolises.

Now the sea's city builders are under siege. The ocean bottom might be the last place you'd think to be troubled by a climate out of kilter. But recently scientists have found that reefs are taking the brunt of the warming atmosphere. Some 30 percent of coral reefs are already irreparably damaged, thanks mainly to rising sea-surface temperatures, which hampers the coral's ability to gather nutrients. Another 30 percent may be poised for collapse. The reefs of the Seychelles never recovered from a 1998 heat surge in the Indian Ocean, another study says. Ten species of fish are either extinct or on the brink. Overall, the variety of marine life among the reefs has fallen by half. As reefs go, so go the oceans.

A coral is one of nature's odder couples: a plant inside an animal. The animal, a tiny polyp, shelters a tinier plant (an algae called zooxanthellae), which returns the favor by sharing the energy it produces through ...