Described as a "one in a thousand year event", the bleaching, which killed off vast swathes of reefs across the globe, has not been repeated to anything like the same extent in the past six years.

"Recovery should continue provided there are no major climate shifts in the next few decades," scientists said in a summary of the 2004 edition of Status of Coral Reefs of the World, released at the IUCN World Conservation Congress in the Thai capital.

"However, the recovery is not uniform and many reefs virtually destroyed in 1998 are showing minimal signs of recovery," they said.

The full report, which says 58 percent of the world's coral reefs are now endangered, is to be made public next month.

Humans continue to represent the single biggest threat to coral reefs, some of the most spectacular places on earth populated with some of nature's weirdest and most wonderful creatures.

About 100,000 species living in and around coral reefs have so far been logged, although some scientists believe the real total may top 2 million.

In particular, the report cited sedimentation, land-based pollution and over-fishing as the biggest threats to the ecosystems.

Conversely, threats from nature seem to be easing off.

"Pressures on coral reefs from coral predators such as the crown of thorns starfish and coral disease appear to have stabilised or even reduced," the report said.

Reefs in South and Southeast Asia, where pressures from booming populations are at their most severe, are those struggling hardest to recover.