JEJU, South Korea — Scientists and local divers are raising fresh concerns over the health of South Korea’s distinctive soft-coral communities around Jeju Island, where colonies are showing signs of another severe “slumping” event linked to increasingly stressful marine conditions.

The phenomenon has alarmed researchers because soft corals are an important foundation of Jeju’s underwater ecosystem, supporting marine biodiversity and contributing to the livelihoods of traditional coastal communities.

Soft Corals Are Collapsing

Unlike hard corals, soft corals do not possess rigid calcium-carbonate skeletons. Their upright structure depends partly on internal fluid pressure.

When environmental conditions disrupt that balance, the colonies can lose their shape, sag toward the seabed and eventually break apart. Scientists have described this process as “slumping.”

Researchers first documented a widespread slumping event around Jeju in 2024. New observations indicate that the problem is appearing again this year, raising concerns about repeated environmental stress reducing the corals’ ability to recover.

Rising Heat Is Increasing the Pressure

Marine conditions around the Korean Peninsula have changed significantly in recent years.

Researchers say prolonged high water temperatures, heavy rainfall and changes in salinity may all contribute to stress on Jeju’s soft corals. Scientists are also watching the potential influence of the El Niño climate pattern, which could bring additional extreme weather and heavy rainfall.

South Korea has experienced exceptionally hot conditions this year, while periods of intense rainfall have affected the southern part of the peninsula.

Scientists caution that the precise causes of the latest coral decline still require additional investigation rather than attributing every change to a single factor.

A Critical Marine Habitat

Jeju’s soft-coral communities occupy an unusual ecological position because they represent coral ecosystems near the northern edge of coral distribution in the East China Sea.

The underwater coral gardens provide habitat for marine organisms and form part of an ecosystem that supports wider biodiversity around the island. The coral communities are also located within protected areas and are recognized for their ecological importance.

Scientists fear that continued degradation at the base of this ecosystem could eventually affect other marine species.

Traditional Divers See Changes Underwater

The concerns are not limited to laboratories.

Jeju’s haenyeo, traditional women divers who collect seafood from coastal waters, have reported changes in marine conditions and declining catches.

Some divers say species that were once plentiful have become harder to find, while unusually warm water has affected the seabed and the availability of marine life. Their observations provide an important local perspective on the ecological changes taking place beneath the surface.

For communities that depend on the sea for income and food, coral deterioration could therefore have consequences beyond conservation.

Scientists Call for Long-Term Monitoring

Researchers are urging authorities to establish stronger and more consistent monitoring systems.

The Korea Institute of Ocean Science and Technology has previously described the slumping phenomenon scientifically and emphasized the need for additional research to determine exactly how environmental stress causes the coral colonies to collapse.

Authorities responsible for marine conservation are also planning further investigations into the scale of this year’s damage.

Scientists say repeated observations are particularly important because occasional surveys cannot fully capture whether coral communities are recovering, deteriorating or adapting to changing conditions.

Climate Change Could Magnify the Problem

The situation around Jeju reflects a broader global concern.

Marine heatwaves are placing increasing pressure on coral ecosystems worldwide. Warmer oceans can stress corals directly while also interacting with rainfall, storms, salinity changes and other environmental factors.

For Jeju’s soft corals, the combination could be especially serious because the colonies already live close to the environmental limits of their geographic range.

Researchers therefore see the island as an important natural laboratory for understanding how temperate coral communities respond to rapidly changing ocean conditions.

A Warning for Jeju’s Marine Future

The renewed slumping observed in 2026 has given scientists and conservationists little room for complacency.

If repeated episodes occur before coral colonies have fully recovered from previous damage, the ecosystem could gradually lose its resilience. That could affect not only the corals themselves but also fish populations, biodiversity, tourism and traditional fishing communities.

For now, researchers are focusing on documenting the changes and determining the precise combination of environmental factors responsible.

The unfolding situation around Jeju offers a stark reminder that climate-related changes are not confined to distant tropical reefs. Even relatively unusual coral communities in the waters of South Korea are increasingly showing signs of stress as ocean conditions change.