In April 2025, marine scientist Sanghoon Yoon descended into the waters off Beomseom Island, a small outcrop on South Korea's Jeju Island, and found the soft corals thriving—their polyps glowing purple, pink, red, and orange in the filtered light. But beneath that relief lay a haunting question: would those same corals survive what 2026 might bring?
A year earlier, in 2024, those same waters had witnessed what scientists are calling a "slumping" event, a phenomenon previously unseen in soft coral populations. The corals lost their shape, drooped, and died in vast numbers, shocking even specialists who study marine ecosystems for a living. The culprit, researchers believe, was a toxic combination of record heat and shifting water chemistry. Jeju's seas reached 30 degrees Celsius (86 degrees Fahrenheit) during the summer—well above the typical 24°C average—while simultaneously experiencing changes in salinity and water quality, all amplified by record rainfall that year.
The alarm bells sounding around Jeju matter far beyond the island itself. The soft corals are not merely decorative; they anchor an entire marine ecosystem that supports fisheries, livelihoods, and a cultural heritage spanning generations. The haenyeo—a community of traditionally trained women who free-dive to harvest marine resources—depend on healthy waters. Tourism built around the island's underwater beauty also hangs in the balance. When Anna Jöst Kim, a coral scientist at the Korea Institute of Ocean Science and Technology, first saw photos of the drooping and dying corals sent by the advocacy group Paran Ocean Citizen Science Center, she and her husband, Taihun Kim, a colleague researcher, launched an urgent investigation. Their findings, published in Nature Scientific Reports, raised hard questions about the future of these ecosystems.
What makes the 2024 event particularly startling is how little scientists understand it. "We are aware that hard corals go through bleaching, but that's a completely different scenario from what happens to soft corals," Yoon observed after his dive. Hard corals bleach when heat forces out their symbiotic algae; soft corals appear to respond to thermal and chemical stress in entirely different ways. Further research is still needed to pinpoint the exact mechanisms at play, researchers acknowledge. The good news is that widespread slumping did not recur during 2025 or in the early months of 2026, suggesting the corals may be more resilient than feared—or that conditions simply did not align to trigger another event.
Yet worry persists. A "Super El Niño" has been predicted for later in 2026, potentially bringing the same kind of ocean warming and atmospheric disruption that set off last year's slumping. Scientists and conservationists are watching carefully, documenting the health of the corals around Beomseom and other sites, preparing for what might come. Taihun Kim spoke of the urgency driving his team's work: "We want to make it public so people are aware of these problems." The soft corals of Jeju Island have become an early warning system for the ocean itself—a barometer of how marine life responds when heat and chemistry collide.