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Mar. 10, 2015 - Updated 04:16 UTC

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Okinawa's 'Miracle Coral'

Feb. 20, 2017

The world's coral reefs are under threat due to rising water temperatures, but a new discovery in Okinawa could reverse the tide.

Coral reefs provide marine life with vital habitat and spawning grounds. Known as 'the cradle of life in the ocean,' experts say one in 4 of the world's marine creatures rely on them for their survival.

Now coral reefs are threatened by rising water temperatures, which lead to bleaching, a process that turns them white and eventually kills them. But findings by a marine biologist in Okinawa may help preserve coral reefs and save oceans from crisis.

Sekiseisyouko, the largest coral reef in Japan, used to be a paradise of colorful coral, and had fish swimming everywhere. But more than 90 percent of it has succumbed to bleaching

The devastation of coral reefs around the world is blamed on the rise of ocean temperatures last year. During the summer, waters near Ishigaki topped 30 degrees Celsius, and the extremely-high temperatures continued for nearly 2 months.

Within the tissue of corals there's a phytoplankton named zooxanthellae. It feeds the coral and gives them color, but when coral has to endure rising water temperatures and strong sunshine, their tissue loses zooxanthellae. This causes 'coral bleaching,' and eventually death.

Bleached corals are seen throughout the sea of Okinawa. But right next to the bleached ones, an NHK team observed some that still had their original color. The corals that did not suffer from bleaching were grown at a farm in Okinawa.

Koji Kinjo is an expert in coral farming. He's been working to restore marine invertebrate to the ocean for nearly 20 years. Coral that do not bleach are Acropora tenuis, and they are abundant in Okinawa. Kinjo spent years adapting them to withstand a harsh environment.

He had a eureka moment at an event to teach about coral spawning 7 years ago. Kinjo moved coral from a deeper part of a water tank to a shallower place, so that children could observe the spawning process more easily. Many of the coral bleached and died because of exposure to sunlight, but some recovered.

He selected and bred the surviving corals and moved them to an even shallower place, allowing them to gradually get used to the new environment. He repeated the process over a period of 4 years and found that his coral didn't bleach, even when exposed to intense sunlight.

Kinjo tried replanting them at sea, and found they could withstand warm water temperatures. He had succeeded in creating coral that were immune to bleaching -- something that was unprecedented.

"It's like a miracle happening. I've been farming corals for 18 years, but nothing like this has ever happened. It's miraculous," Kinjo says.

Research is underway to identify what exactly prevents coral from bleaching.

Yoshikatsu Nakano, a coral reef expert at the University of the Ryukyus, and a team of researchers have been comparing and analyzing coral that do and do not bleach from a variety of angles.

They found no difference between them in terms of the zooxanthellae in their tissue. But they found something that was different in the coral that didn't bleach: plenty of a bacterium called endozoicomonas.

"Something is happening to the bacteria. It's become increasingly evident that the bacteria have something to do with the intensity of bleaching. It's still a small but an important step," says Nakano.

Coral that resist bleaching were created in Okinawa and Kinjo hopes to grow more of this type of coral, and help restore the coral reefs in his hometown.

"When I was a child diving in the waters of Okinawa, it was like watching full-color, high definition TV. But when I dove into the water just recently, it was almost like black and white. But my recent experiment has given me confidence that we can bring back life, marine creatures," he says. "This may be a dream but we definitely want to win the battle on climate change."

The bleaching is now a growing global concern but this discovery could be part of a solution to revive coral reefs around the world.