The forest vanishes
Off the coast of Gijang, a significant portion of the underwater area has changed. What were once dense forests of kelp, primarily species like Ecklonia cava and various types of Sargassum, are now rocky plains with little vegetation. This widespread devastation, known locally as a "whitening event," covers about 37.1% of Gijang's coastal waters. The primary cause of this large-scale deforestation is the overgrazing by sea urchin populations.
The ecological shift began with a classic trophic cascade. The removal of natural sea urchin predators—such as certain species of starfish, crabs, and fish like the California sheephead—allowed herbivore numbers to swell unchecked. With few predators to control their population, the sea urchins, particularly species like Strongylocentrotus intermedius and Mesocentrotus nudus, began to consume the kelp forests at an unsustainable rate. Kelp forests are productive ecosystems, providing food and habitat for hundreds of other marine species. Their disappearance leads to a sharp decline in local biodiversity. The resulting "urchin barrens" are stable, but far less productive, ecosystems dominated by rocky substrate covered in crustose coralline algae.
A persistent barren state
An urchin barren is an example of an alternative stable state in an ecosystem. Once established, it strongly resists returning to its previous kelp-dominated state. The dense populations of urchins actively graze away any new kelp that tries to settle, effectively trapping the ecosystem in its barren phase. This makes recovery difficult even if the initial problem, the lack of predators, is addressed. The barrens can persist for decades.
In response, South Korea has initiated one of the world's largest kelp restoration projects. Since 2009, the Korea Fisheries Resources Agency (FIRA) has been working to restore tens of thousands of hectares of kelp forest nationwide. In Gijang, projects focus on creating "sea forests" by transplanting seaweed, dispersing zoospores (kelp seeds), and improving the substrate. A part of these efforts involves the physical removal of sea urchins to give the kelp a chance to establish itself. Studies have shown that drastically reducing urchin density can allow a barren area to return to a healthy kelp forest within months. The Gijang Seaweed Breeding Convergence Research Center is also developing new ecological platforms and eco-friendly attachment substrates to aid in the restoration process.