Coral in the northwest part of the South China Sea has experienced a rare mass bleaching event, according to a Chinese scientist surveying the reefs.

An analysis released Aug. 28 by the National Oceanic and Atmospheric Administration in the U.S. shows that the Beibu Gulf in the South China Sea, as well as areas surrounding areas, are facing extreme coral bleaching alerts that could decimate the health of aquatic ecosystems.

In a survey earlier the same month, Li Yuanchao, an associate professor at Hainan Academy of Ocean and Fisheries Sciences, found that coral in shallow areas of the Beibu Gulf off the northwest coast of the island province of Hainan were “severely bleaching.”

“100% of the coral in shallow waters was found to be whitening, and the coral mortality rate was over 86%,” Li told Sixth Tone, adding that massive coral bleaching was also detected by researchers around Weizhou Island, in the middle of the gulf, between July and August.

When corals are stressed by overheating, they release the algae that inhabit them, resulting in the bleaching effect. While some bleached corals can later recover, many end up dying.

“A coral bleaching event of this scale is very rare in this area,” Li said, adding that this year’s El Niño — a naturally occurring climate phenomenon characterized by unusually warm water in parts of the Pacific Ocean — played a major role.

During the summer, warm seawater settled in the Beibu Gulf, and the lack of continuous flow and exchange with colder water masses resulted in elevated sea temperatures, Li said.

“In previous years, the (seawater) temperature was around 27 or 28 degrees, but this year it rose above 30 degrees… The water is hot even 20 or 30 meters down,” he said. “Very few typhoons reached the Beibu Gulf this year, so the water temperature has remained high.”

China’s National Marine Environmental Forecasting Center reported that temperatures in the South China Sea were 0.6 degrees higher this week compared with a historical average.

“According to the NOAA’s forecast, coral bleaching will only become more serious if there’s no cooling event, such as a typhoon, on the horizon,” Li said.

Despite some conservation efforts, coral is severely declining, both in China and around the world, due to human activity and climate change.

Global warming poses an existential threat to the world’s coral reef ecosystems. The U.N. Intergovernmental Panel on Climate Change found substantial evidence that a majority of warm-water coral reefs would disappear even if heating were limited to 1.5 degrees Celsius.

Meanwhile, Taiwan this year reported its most severe bleaching event on record due to overheating. And in March, scientists determined that Australia’s Great Barrier Reef had suffered its third massive bleaching event in five years.

In 2017, researchers found that warming in the northern part of the South China Sea had caused mass coral bleaching, also due to a historically strong El Niño, killing 40% of the coral on Dongsha Atoll.

“The coral bleaching west of Hainan was sudden this year,” Li said, adding that corals off the island’s west coast will have an especially difficult time recovering after the bleaching event.

“All we can do is continue to track and monitor — there’s no way to treat (the coral bleaching) because the scale is too massive,” the researcher said.

Editor: David Paulk.

(Header image: Kyodo News via Getty Images/People Visual)