"We have reason to believe that if climate changes continue due to the carbon dioxide that is being pumped into the atmosphere, the temperatures at ground level and in the oceans will go up," Dr. Carl Lundin, head of the marine program of the Swiss-based World Conservation Union (IUCN), said.

"So virtually all the coralline islands have a decent chance of disappearing in 50 years," Lundin told Reuters in Victoria, the capital of the Seychelles.

Coral reefs are among the most diverse and productive communities on earth. Found in warm, clear, shallow waters of tropical oceans worldwide, reefs have functions ranging from providing food and shelter to fish and invertebrates to protecting the shore from erosion.

Many coral reef organisms can only tolerate a narrow range of environmental conditions and are very sensitive to damage from environmental changes such as rising temperatures which can cause bleaching and eventual death.

Lundin said sustained warming up of ocean currents which followed the El Nino effect in 1998 resulted in bleaching and widespread damage to corals in the Indian Ocean.

"So a very large region has been affected and an awful lot of damage has been caused by the temperature increases which varied from one to two to generally up to five degrees Celsius."

According to Lundin, the Seychelles' coralline islands of Amirantes, Aldabra, Bird island and Denis island which support unique ecosystems are seriously threatened.

"These islands are made of fossil reefs that have been raised out of the water but as erosion continues, they are likely to be gnawed away," said Lundin.

Lundin said there was some coral recovery with islands which lost up to 100 percent of their coral cover in 1998 having regained between two and 20 percent of their cover.