An Oceanic and Volcanic Oasis
Dokdo is a set of volcanic islets that emerged from the sea between 4.6 and 2.5 million years ago. The two main islets, Dongdo (East Islet) and Seodo (West Islet), along with 89 smaller surrounding rocks, are the visible peaks of a massive underwater volcano rising over 2,000 meters from the seafloor. The total land area is a mere 187,554 square meters. The bedrock consists of porous and easily eroded alkaline volcanic rocks like andesite and tuff.
The waters surrounding these islets are a dynamic meeting point for major ocean currents. The warm, saline East Korea Warm Current, a branch of the Tsushima Current, flows northward and collides with the cold, nutrient-rich North Korea Cold Current flowing south. This confluence, known as a polar front, creates a highly productive marine environment, rich in the plankton that forms the base of the local food web. The interaction of these currents with the island's topography also causes upwelling, further increasing biological productivity in what is sometimes called the "Dokdo effect." The South Korean government designated the islets as Natural Monument No. 336 in 1982 to protect this unique environment.
A Crossroads for Life
The rich waters and isolated landmass of Dokdo support many different species. The islets are a critical stopover for migratory birds, with over 180 species recorded. Dokdo is a breeding ground for streaked shearwaters (Calonectris leucomelas), black-tailed gulls, and Swinhoe's storm petrels. The streaked shearwater, a burrow-nesting seabird, has its only confirmed Korean breeding colony here.
The intertidal zone, the area exposed between high and low tides, is dominated by mollusks and crustaceans. Surveys have identified dozens of species, with mollusks like limpets and turban shells making up nearly 70% of the species count. Arthropods such as barnacles and shore crabs are also common residents. The subtidal zones host over 250 species of algae and more than 520 species of marine invertebrates. A large habitat of the coral Dendrophyllia cribrosa, a species whose numbers are declining elsewhere, was found 25 meters below the surface. The mixing of warm and cold currents allows for the co-existence of fish species typical of different temperature zones, such as pollock from colder waters and yellowtail from warmer seas.