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Ashizuri-Uwakai NP, Kochi
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In 1970, Tatsukushi Bay became Japan’s first designated underwater park, protecting its coral-rich sea. The legal name changed to “marine park” in 2010, but the pioneering designation began here.
Tatsukushi’s surrounding sea is home to 105 coral species—a remarkable variety for a small bay in a temperate climate. The warm Kuroshio Current helps create this mix of marine life.
In Minokoshi Bay, a shikoro coral colony measures about 45 by 26 meters and is one of Japan’s largest. January surface water averages about 17°C, and the colony is a Kochi Prefectural Natural Monument.
Tatsukushi-area menus feature kameno-te, or “turtle hands,” in miso soup. They look like little shells, but these rock-clinging animals are barnacle relatives of crabs and shrimp—not mollusks.
Tosashimizu Geopark reports 384 nudibranch species in Tatsukushi’s waters. These often tiny, vividly colored sea slugs add another astonishing layer to a bay already known for its diverse corals.
The twisted layers of a formation called “Shibori-maku,” or “gathered curtain,” record ancient earthquake shaking: wet seabed sediments liquefied and folded before hardening, about 17 million years ago.
Tatsukushi’s rocks preserve what ancient animals did, not just what their bodies looked like: researchers identify fossil burrows made by shrimp-like sand diggers and feeding trails left by worms.
Local names turn the coast into a natural gallery: “Big Bamboo” and “Little Bamboo” describe long, jointed rock ridges, while “Ranma Rock” recalls the decorative openwork panel above a traditional Japanese doorway.
A local story says the famous monk Kūkai, also known as Kōbō Daishi, left this rugged coastline unseen—giving nearby Minokoshi its name, often translated as “left unvisited.” It is a place-name legend, not documented history.
In a 2012 Tatsukushi project, forestry workers, fishers, and divers joined forces to make spawning beds for bigfin reef squid (moika) from thinned cedar branches—a creative link between forest care and sea life.
The 2001 torrential rain sent so much sediment into Tatsukushi Bay that many corals died. Residents, scientists, and officials worked across the mountains, rivers, and sea; the Ministry of the Environment judged the recovery goal met by the end of fiscal 2014.
