"Scientific reports are indicating we will have no corals left by 2050," Jude Bijoux, manager of the Seychelles Centre for Marine Research and Technology, told Reuters.

"We lost 90 percent of them in 1998 and the little that was left is recovering slowly and is apparently under frequent threat."

In 1998, the El Nino weather phenomenon, which occurs when sea surface temperatures rise substantially, had devastating effects.

According to researchers, 33 vast sites in the Indian Ocean where corals died in 1998 may suffer repeated damage every five years -- roughly corresponding to El Nino cycles -- by 2025 if not sooner.

Many scientists believe global sea temperatures are rising because increasing fossil fuel emissions from cars, industry and other sources are trapping the earth's heat. Other threats to reefs include pollution, over-fishing, coastal development and diseases.

Bijoux said there was now a global consensus that mass destruction of corals caused by bleaching as a result of rising sea temperatures was occurring more frequently compared to 20 years ago.

He said serious destruction of many of the world's reefs had occurred four times in the last 23 years -- in 1983, 1998, 2002 and 2003.

Scientists predict that most of the Indian Ocean's coralline islands -- islands made up of dead corals -- will disappear within 50 years, as living reefs that surround and protect them are degraded.

The Seychelles archipelago of 120 islands, located off the southeast coast of Africa, has only 65 coralline islands with the remainder being granite.

Maldives is made up entirely of coralline islands.

"These results are not good. This will have serious impacts on coral recovery and our efforts to protect our corals," said Ronny Jumeau, Seychelles environment minister.

He said efforts to protect reefs should still be made, adding that corals found in protected areas were showing some signs of recovery.