Kenyan-based Obura, a researcher with CORDIO (Coral Reef Degradation in the Indian Ocean), said there had been "catastrophic mortality" among shallow-water coral reefs off East Africa following a 1997-98 El Nino event that pushed up sea surface temperatures in the Indian Ocean.

"There was a 70 to 75 percent mortality during the El Nino in 1997-98 in shallow water reefs off East Africa," he said.

Models suggested that the events of 1998 could be repeated on a regular basis in 20 to 50 years' time because of rising sea surface temperatures.

Such a scenario would have grim consequences for the region's rich corals, which are crucial to East Africa's tourist industry, as they are a magnet for scuba diving enthusiasts.

"They (corals) can survive a bleaching. It is akin to a fever in mammals," Obura said. But if the stress was too great on the corals, then they died off.

Coral bleaching refers to the whitening of corals from a loss of pigment.

This is a signal of ecosystem stress which can be triggered by sedimentation, pollution, or rising temperatures, among other factors still being disentangled by scientists.

Scientists maintain global temperatures are rising rapidly because fossil fuel emissions from cars, industry and other sources are trapping the Earth's heat.