50% of Jeju's Beomseom Coral Cluster Struggles as Ocean Warming Slumps Soft Corals

For climate observers, Jeju's slumping soft corals are a living sentinel of ocean warming. Unlike heat-tolerant hard corals, these UNESCO-listed soft corals depend on internal fluid pressure that warm, disrupted waters destabilize, making them an early indicator of broader marine ecosystem stress. With half of one Beomseom cluster already struggling in 2026 and El Niño threatening through September, the event signals what repeated marine heat stress looks like in temperate waters.

Off the southern coast of Jeju Island, a slow-motion ecological collapse is alarming divers, scientists, and government agencies. South Korea's UNESCO-listed soft coral colonies, long celebrated as underwater gardens and a designated national monument, are slumping over and dying for a second substantial year, according to a Reuters report published September 7, 2026. The Paran Ocean Citizen Science Center, a volunteer diving group that monitors the corals around mostly uninhabited islets south of Jeju, says roughly half of one coral cluster off the islet of Beomseom has been struggling in recent months. The phenomenon mirrors a large-scale slumping event in 2024, which researchers at the Korea Institute of Ocean Science and Technology (KIOST) documented for the first time in a May article in Scientific Reports.

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The Paran Ocean Citizen Science Center, a volunteer diving group that monitors the corals around mostly uninhabited islets south of Jeju, says roughly half of one coral cluster off the islet of Beomseom has been struggling in recent months.

The vulnerability is structural. Unlike hard corals supported by rigid calcium carbonate skeletons, soft corals rely on internal fluid pressure to keep themselves upright. When environmental conditions change — particularly rising sea temperatures and altered water chemistry — that hydrostatic balance can be disrupted, causing the corals to sag, collapse, and in severe cases die. Researcher Kim Taihun, who co-authored the Scientific Reports paper with colleague Anna Beate Jöst, explained that repeated large-scale slumping creates a destructive cycle: corals partially recover, then many break off and deteriorate again, steadily eroding their capacity to recover. He said this year's event looks similar to that of 2024 but could worsen if high water temperatures persist through September and the El Niño weather phenomenon intensifies.

For local communities, the collapse is both ecological and cultural. Haenyeo diver Ko Myeong-hyo, who began diving off Jeju six years ago, described watching the coral garden collapse and turn white as disorienting. The sea women and other divers have long depended on these waters for seafood and tourism, and the coral gardens around Mun Island are a famous scuba diving destination. The Paran Ocean Citizen Science Center's underwater monitoring operations in August 2026, including a photo of a tropical pink sea anemone attaching itself to coral near Mun Island, have provided visual evidence of a shifting ecosystem, with tropical species moving into temperate waters as ocean temperatures rise.

Government agencies are beginning to respond. Korea Heritage Service, which manages the soft coral colonies designated as a national monument, said in an email that it has monitored the situation this year and will maintain long-term research to identify the causes of the changes. The Oceans Ministry, which oversees marine protected species and areas including soft corals, added that it plans a detailed investigation to gauge the scale of damage. Kang Do-hyung, principal research scientist at KIOST and former Oceans and Fisheries Minister, was seen checking corals at the Jeju Tropica lab on Jeju Island in August 2026, underscoring the scientific attention the events are drawing. Notably, a photograph of closed-cell extruded polystyrene foam particles washed ashore on a Jeju beach also highlights additional pollution pressures that may compound climate stress on coastal ecosystems.