'Slumping' South Korean Corals Raise Alarm Among Divers and Scientists

When Ko Myeong‑hyo first slipped beneath the waves off Jeju Island six years ago, she was drawn by the dazzling reds and oranges of the soft‑coral gardens that dotted the sea floor. Back then, the reefs seemed almost invincible, a living tapestry that supported the island’s famed haenyeo “sea women” and the bustling tourism trade.

Fast‑forward to September 2026, and the same divers are staring at bleached, wilted formations that look more like wilted lettuce than the vibrant coral forests they once knew. “Watching the coral garden collapse and turn white, it was so disorienting,” Ko says, her voice tinged with the same awe‑and‑fear that first brought her into the water.

The phenomenon—dubbed “slumping” by the Paran Ocean Citizen Science Center, a volunteer group that patrols Jeju’s UNESCO‑listed soft‑coral sites—has resurfaced with a vengeance. Soft corals, unlike their hard‑shelled cousins, lack a rigid calcium carbonate skeleton. They rely on an internal hydrostatic pressure to stay upright, so when water temperatures climb or salinity shifts, that delicate balance can tip, causing the organisms to sag, break, or even die.

Recent surveys around the uninhabited islets south of Jeju, especially near Beomseom, show that roughly half of a once‑thriving cluster is now struggling. “If another large‑scale slumping happens, the corals may partially recover, only to break off again,” explains Kim Tai‑hun, a researcher with the Korea Institute of Ocean Science and Technology (KIOST). “Their capacity to bounce back just keeps dwindling.”

Kim and his colleague Anna Beate Jöst were the first to document a similar event in 2024, publishing their findings in Scientific Reports. This year, they fear the situation could worsen. A lingering El Niño pattern may keep water temperatures high through September, while the same system could also spawn typhoons and torrential rains that further stress the fragile ecosystems.

Adding another layer of complexity is the influx of fresh water from China’s Yangtze River, which dilutes the seawater around Jeju and messes with salinity levels. Combined with an unprecedented heatwave that has baked the Korean peninsula this summer, the conditions are ripe for coral stress.

For the people who depend on these reefs—divers, fishers, and even the broader marine food web—the stakes are personal. Soft corals act as nurseries, sheltering countless fish species and supporting the seaweed forests that form the backbone of Jeju’s marine ecology. “If the base ecosystem collapses, the entire marine ecosystem could follow,” warns Yoon Sanghoon, an environmental expert with Paran.

South Korea’s heritage officials have taken note. The Korea Heritage Service, which designates these soft‑coral colonies as a national monument, says it will continue long‑term monitoring. Meanwhile, the Ministry of Oceans and Fisheries has pledged a detailed investigation to gauge the extent of damage and, hopefully, devise mitigation strategies before the next wave of warming arrives.

In the meantime, the haenyeo keep diving, documenting, and sharing their observations, hoping that the collective data will paint a clearer picture of what’s happening beneath the surface. Their hope is simple: that by sounding the alarm now, the world can act before these underwater gardens fade completely into memory.