Egg-sperm bundles, like tiny balls of snow, are spewed into the Caribbean off the coast of Puerto Rico during August spawning of elkhorn coral. (SECORE/Ramon Villaverde/Canadian Press)

Lower-than-feared sea temperatures this summer gave a break to fragile coral reefs across the Caribbean and the central Gulf of Mexico that were damaged in recent years, scientists said Thursday.

Unusually warm water in recent years has caused the animals that make up coral to expel the colorful algae they live with, creating a bleached colour. If the problem persists, the coral itself dies — killing the environment where many fish and other marine organisms live.

"We dodged a bullet this year. The good news is that temperatures didn't get quite warm enough for there to be a large-scale bleaching problem," said C. Mark Eakin, co-ordinator of the National Oceanic and Atmospheric Administration's Coral Reef Watch network. He was among scientists gathered in Puerto Rico's capital for a meeting of the U.S. Coral Reef Task Force.

The worst coral bleaching in the region's recorded history occurred in 2005, when hot seas caused bleaching of as much as 90 per cent of corals in the eastern Caribbean, with more than half of that dying.

In July, the Coral Reef Watch network warned that high temperatures this year might lead to severe coral problems because sea surface temperatures in parts of the Caribbean were unusually hot.

Eakin said the threat had passed for 2009, since temperatures are now cooling, but the problem could return.

"We're seeing little signs of coral recovery in the Caribbean, where the damage has been like a ratchet wrench clicking down and staying there," Eakin said. "Temperatures could be severe enough next year."

Reef-building coral is a fragile organism, a tiny polyp-like animal that builds a calcium-carbonate shell around itself and survives in a symbiotic relationship with types of algae — each providing sustenance to the other. Even a one-degree rise in normal maximum sea temperatures can disrupt that relationship.

Bleaching can occur when sea temperatures rise just a few degrees above average in the warmest summer months. Bleaching that lasts more than a week can kill the organisms, since they rely on the algae for sustenance.

Some coral bleaching was recorded this year in the Cayman Islands, according to Eakin and scientists in the British Caribbean dependency.

Croy McCoy, a senior researcher with the islands' Department of Environment, told The Associated Press that officials are still calculating the damage to local reefs.