It is a two-hour boat ride from Yeosu, Jeollanam-do, to Baekdo in Dadohaehaesang National Park.

We approached the island closely on a small boat.

[Chang Sun-yi / Reporter: This is the waters off Baekdo. Access is restricted so human hands have barely touched it, but as water temperatures rise, the marine life living here is changing.]

A professional diving team descended to a depth of 20 meters.

Spreading out like fans, the endangered orange sea gorgonian and soft corals, once seen only in Jeju's waters, catch the eye.

[Ahn Jung-kwan / Dr., Marine Research Center, National Parks Research Institute: Subtropical soft coral species such as the red finger sponge, thorny finger sponge, and wire coral, which were previously reported to grow only in Jeju Island, have moved quite far north.]

Soft corals have been expanding their habitats for three years. The long-branch gorgonian, a natural monument, is also visible.

The long-branch gorgonian is one of the climate change indicator species showing the subtropicalization of the sea.

Other climate change indicator species, such is the yellow damselfish, sapphire damselfish, and boxfish, were also confirmed in this survey.

Rising water temperatures are the direct cause.

[Kim Dae-won / Senior Researcher, Korea National Park Service: Sea surface temperatures around the Korean Peninsula have increased by about 1.36 degrees Celsius over the past 58 years, and warming is progressing at a very rapid pace, about 2.1 times the global average.]

In a 2014 survey, Baekdo was the island where the most seaweeds were identified among 11 islands in the South Sea, with 117 species.

However, in 2024, seaweeds decreased to 97 species.

Researchers analyze that as water temperatures rise, so-called marine desertification is progressing, and the population of marbled spinefoot, which feeds on seaweed, is increasing, causing the "sea forest" to disappear.

Sea forests, which are seaweed communities, absorb 337 tons of carbon dioxide per square kilometer.

In the East Sea, where water temperatures are rising nine times faster than the global average, artificial sea forests are being created, and the underwater scenery of the South Sea on the Korean Peninsula is also changing rapidly.

Looking into the South Sea... The Disappearing "Sea Forest" (Oct. 11, 2026, 8 News)

(Reported by Chang Sun-yi | Written by Bae Jun-hwi | Filmed by Yang Ji-hoon | Edited by Park Chun-bae | Footage provided by Korea National Park Service | Produced by SBS Digital News)