WASHINGTON - Some coral populations already have genetic variants necessary to tolerate warm ocean waters, according to a study calling for the spread of such genes to help corals survive global warming.

"Our research found that corals do not have to wait for new mutations to appear," said study author Mikhail Matz of the University of Texas. "Averting coral extinction may start with something as simple as an exchange of coral immigrants to spread already existing genetic variants."

Coral larvae can move across oceans naturally, but humans could help by relocating adult corals to jump-start the process, Dr Matz said in a statement on Thursday.

Some corals have higher tolerance for elevated temperatures, though until now no one understood why some adapted differently from others.

In the new study, researchers crossed corals from naturally warmer areas of Australia's Great Barrier Reef with corals from a cooler latitude nearly 500km to the south.

They found that coral larvae with parents from the north, where waters were about 2 deg C warmer, were up to 10 times as likely to survive heat stress, compared with those with parents from the south. Using genomic tools, the researchers identified the biological processes responsible for heat tolerance.

Furthermore, the study showed that when corals from the north cross with corals from the south, they can pass on their tolerance for heat to their offspring. The findings were published in the US journal Science.

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