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Japanese authorities, researchers search for solution to dying coral reefs

Sep. 26, 2017

Coral reefs play an important role in marine ecosystems, providing habitats and spawning grounds for marine life. A survey conducted by Japan's Environment Ministry last year revealed that the country's largest coral reef, located in Okinawa, is dying.

Marine biologists say more than 300 varieties of corals live in the area. But this ecosystem is changing dramatically. A government survey conducted last year found that 90% of the reef had lost its color, in a process called coral bleaching.

Today, large areas have darkened. Many corals that had lost color last year are now only dead remains. Scientists think the cause could be high sea temperatures. Corals get their nutrients from zooxanthellae, which live inside them and carry out photosynthesis. When the water temperature rises above 30 degrees Celsius, some zooxanthellae may exit the coral, while others remain inside but stop photosynthesizing. The coral then isn't able to receive enough nutrients and eventually dies.

A closer look reveals why the reef appears dark now. Part of it is covered with seaweed. Another part has a cluster of micro-organisms. In this state, recovery is difficult because new corals can't take root.

Scientists say reefs face a rising level of danger. Yoshikatsu Nakano of the Reef Preservation Research Group says "On land, there's desertification. Lakes are drying up, and deserts are expanding. Coral reefs are about to enter a similar crisis period. Since the frequency and scale of bleaching is going up, it is clear that coral reefs are diminishing."

The shrinking of coral reefs is impacting fish and other creatures. Most of the fish sold in Okinawa comes from near the reef. Fishermen say their catches have been dropping. "The amount has been going down every year. Lobsters, groupers, and sea bream -- they are all from around the coral reef," one of them says.

Efforts are being made to revive coral reefs, including a project that was launched by the Fisheries Agency with the help of local fishermen. The egg and sperm of a coral fertilize in water to become a larva. The larvae reach the sea floor and grow to form reefs. But before that can happen, many get eaten by other animals or swept away by ocean currents. It's believed less than one percent of larvae survive.

The project aims to tackle this issue by covering coral reefs in enclosures. An experiment was held in May. Living coral is placed so that it will spawn. At 8PM the next day, spawning starts. About 200,000 eggs are released inside the enclosure. A week later, researchers check whether the larvae survived.

A calcium carbonate structure has formed around the larvae -- meaning they have taken root and are ready to grow. Blocks where larvae have established themselves are brought back to the sea, where they can eventually form reefs.

"If we revive coral reefs, and then later catch the fish that grow up there, that would be amazing. It would be something we've never experienced before," says a fisherman. "We have high hopes, for us and the next generation," says another.

A survey led by a local university revealed some reefs have escaped the damage of bleaching. It was previously believed corals couldn't live in deep waters, where there's not enough light for zooxanthellae to carry out photosynthesis.

But researchers have found corals living 40 meters below the surface. And because temperatures are low there, they haven't bleached. The research team will look into ways to use them to revive reefs in other parts of the sea. "If corals remain bleached, we will have to find other places that can supply larvae, and deep water will be one of those places," says University of the Ryukyus Associate Professor Saki Harii.

The study is still in the early stages. But researchers are hopeful their efforts can help bring back coral reefs and the sea life that relies on it.