Corals naturally able to survive in the hottest tropical waters may be bred with cousins in cooler seas in the form of a "genetic rescue" that could help them survive the growing threat of global warming, researchers are suggesting.

A study involving scientists at the University of Texas at Austin found that corals inhabiting warm waters around Australia's Great Barrier Reef showed an ability to survive greater increases in temperatures than an identical species from cooler waters just 300 miles to the south.

The finding raises the possibility that deliberately planned breeding efforts could pass on the heat-tolerant genes to help some coral reefs adapt to climate change, the researchers suggest in a study appearing in the journal Science.

"Coral larvae with parents from the north, where waters were about 2 degrees Celsius (3.6 Fahrenheit) warmer, were up to 10 times as likely to survive heat stress, compared with those with parents from the south," the scientists wrote.

While the heat-tolerant genes are likely to eventually spread through natural migration to the stressed corals, there is no reason that process can't be helped along and sped up by human efforts, researchers say.

"These mutations are already there, they just need to be spread out," says UT biologist Mikhail Matz.

The heat-tolerant genes were discovered by researchers attempting to cross-breed a branching coral known as Acropora millepora, found in the northern regions of the Great Barrier Reef, with examples of the same species found further south.

The result was heat tolerance displayed by the offspring of the cross-breeding, they say.

"The take-home message is that the genetic capacity is already there," Matz says.

Such a "genetic rescue" could ultimately be more effective than current proposals that would see adult forms of the species physically shuttled from one area to another.

"Coral larvae can move across oceans naturally, but humans could also contribute, relocating adult corals to jump-start the process," Matz says.

That would require permission from the Great Barrier Reef Park Authority, the researches note.

The researches said global warming was not the only threat faced by the world's coral reefs; pollution and increasing acidification of the ocean are also taking their toll.

Even a genetic rescue would not be "a magic bullet that will safeguard corals from the multitude of stressors they are currently facing," says study co-author Line Bay from the Australian Institute of Marine Science.

Additionally, it wouldn't provide a permanent solution in the face of ongoing ocean warming, the researchers warn.

"Eventually, the corals will run out of genetic variation," Matz says. "But this might buy us time. We might feel safe for the next few decades."