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Growing Coral to Keep a Sea Claim Above Water

The Okinotori Islands poking up from a submerged table reef.Credit...Ministry of Land, Infrastructure, Transport and Tourism. Kanto Regional Development Bureau

TOKYO — Amid warnings that rising sea levels caused by global warming could lead to the disappearance of some entire island states, two tiny uninhabited islets in the Pacific are at the forefront of Japanese research into the preservation and regeneration of coral reefs.

About 1,100 miles south of Tokyo, the Okinotori Islands poke out of a submerged coral reef measuring about seven miles around. But as Japan’s most southerly territory they bring with them a claim to a 160,000-square-mile exclusive economic zone, an area larger than the Japanese archipelago itself.

As long as they stay above water.

Under the United Nations Convention on the Law of the Sea, a claim to an exclusive economic zone depends on the existence of a habitable island landmass. If the islands disappear so does the zone, which in Okinotori’s case is rich in fish and mineral resources and potentially in oil and methane hydrates, a form of solidified methane gas.

China already disputes the Japanese claim, arguing that Okinotori is merely a cluster of uninhabitable rocks. To bolster, literally, its position, the Japanese government has encased the two islets in walls of cement, steel blocks and titanium mesh. It also erected, in 1988, a third, artificial islet with platform supporting a weather monitoring station and a building to house researchers.

Still, over the years, the reef has eroded. Japan’s Fisheries Agency says it is not making a link between rising sea levels and coral depletion. The agency is, however, worried that warmer waters in the area have been preventing the corals from thriving.

Wataru Ando, an expert on coral regeneration, says the health of the Okinotori reef has worsened over the eight years since he started working there. Mr. Ando blames increasingly violent typhoons and a measurable rise in ocean temperature for the deterioration.

Politics aside, if the corals around the islands thrive, so should the islands, Mr. Ando and other researchers say.

Both the Japanese Ministry of Land, Infrastructure, Transport and Tourism and the country’s Fisheries Agency have separately made it a priority to revitalize the corals to protect the economic zone and its resources.

That can be challenging: “The currents around Okinotori Island are strong,” said Norihito Watanabe, a section head at the Fisheries Agency. “It’s a harsh environment.”

So harsh that when the land and infrastructure ministry tried to set a new pier on the reef in March, part of a plan to build a port there, the effort ended in disaster. The concrete structure, 100 feet by 66 feet, capsized, throwing 16 workers into the sea. Seven died.

Research efforts to regenerate the coral have been more successful.

The Fisheries Agency has been applying a method of sexual reproduction developed over the past 20 years by Makoto Omori, member of a Fisheries Agency coral restoration committee and former director of the Akajima Marine Science Laboratory, a private research institute specializing in tropical marine environments.

“Cultivating corals may sound easy, but it’s actually quite difficult,” Mr. Omori said in an interview.

The method, which can produce corals in large numbers, has been used by the Philippines, Palau and Thailand to restore damaged reefs, he said, but its use on the Okinotori reef is the biggest practical application to date.

Implementation has been entrusted to the Fisheries Infrastructure Development Center, a nonprofit research institute based in Tokyo, using Fisheries Agency funds earmarked for Okinotori’s regeneration since 2006.

Researchers from the center transported adult corals by boat from Okinotori to a facility in Okinawa, 680 miles away. Eggs from the corals were obtained by captive spawning and fertilized by sexual exchange on the surface of the water. The resulting larvae and juvenile corals were cultured under laboratory conditions before being returned to repopulate the Okinotori reef.

Mr. Ando, a senior researcher at Fisheries Infrastructure, said the trickiest part of the process was to create the conditions under which the coral larvae would attach themselves to the seaweed-like coralline algae with which coral polyps have a symbiotic relationship.

“You can’t have too much coralline,” Mr. Ando said: “It has to be the right amount. It is a difficult process because factors like water temperature and light need to be exact.”

According to the Fisheries Agency, about 2.15 billion yen, or $19 million, in taxpayer’s money has been spent to breed about 100,000 coral plants using Mr. Omori’s method. Mr. Ando said that about 20 percent of these had survived after their return to Okinotori.

Mr. Ando’s team of researchers has been taking once-a-year trips to transplant the Okinotori Island corals and to monitor the development of previous years’ transplants. “It takes four years for corals to be mature enough to produce eggs,” Mr. Omori said.

Two years ago, researchers reached a milestone in the project when they observed the first generation of laboratory-bred corals reproducing on the reef.

Meanwhile, they have also been trying to identify additional areas of the reef that could provide suitable anchorage for future transplants.

Back in the laboratory they are trying to develop a lower-cost and simpler way to produce coral seedlings and to increase their genetic diversity, to bolster the overall health of the reef ecosystem.

For that purpose, sexual reproduction is far more effective than asexual cloning as a method of reef regeneration, Mr. Omori said. In asexual cloning a fragment of coral, broken off from its parent, develops as a separate replica of the original organism.

“By increasing the number of corals, the number of fish increases, too — so it helps the whole ecosystem,” he said.

Though results have been encouraging, Mr. Omori worries that the scale of the project remains too small to save the Okinotori reef. Since 2009, he said, sensors have shown water temperatures there rising by up to two degrees Celsius, or 3.6 degrees Fahrenheit.

“There may be no Okinotori island 30 years from now due to effects from global warming,” he said. “We need to step up efforts to protect the reef more if we want to keep the area as Japan’s.”

A version of this article appears in print on   of the National edition with the headline: A Coral-Saving Project With Big Money at Stake. Order Reprints | Today’s Paper | Subscribe

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