Minokoshi Coast was added to Your Favorites!
Ashizuri-Uwakai NP, Kochi
Claim this place to tell your story your way.
Minokoshi Bay shelters Japan’s largest shikoro coral colony: an official survey measured it at about 45 m long and 26 m wide. It is a Kochi Prefecture natural monument—and thrives in water whose January average is only about 17°C.
Local tradition says the celebrated monk Kōbō Daishi (Kūkai) never saw this coast because it was so hard to reach. The name stuck: even today, visitors usually arrive by glass-bottom boat from nearby Tatsukushi.
The sandstone is about 20 million years old, but its honeycomb-like pits are still a geological puzzle. Salt weathering from sea spray is thought to be a major cause; scientists say exactly why the holes form in that pattern is not fully understood.
A granite mooring post made in 1920 still stands, while posts carved from Minokoshi’s softer local rock have worn thin or broken away. The contrast turns an old piece of harbor gear into a natural demonstration of erosion.
Look closely and you may spot trace fossils: marks left by ancient creatures, rather than fossilized bodies. An Environment Ministry ranger notes that some resemble worm trails, preserving evidence of animals that once moved through the sediment.
The 2001 southwest Kochi floods sent so much soil into Tatsukushi Bay that the water stayed cloudy and corals across the bay suffered. Yet a government restoration plan reported that Minokoshi Bay’s great shikoro colony had changed little.
One formation is called Tsuzumi Rock after the small hollow in its surface: tap it with your palm and it makes a drum-like sound. The local glass-boat operator shares the curious name and its hands-on origin.
The name recalls a local seafarers’ story: when strong westerlies stopped boats from leaving the bay, crews waited on this flat rock and passed the time with dice or hanafuda playing cards.
Three enormous openings pierce the rock at a spot called Mermaid Palace—the largest erosion hollows on the coast. Local folklore says mermaids once played there, giving this natural sculpture a storybook name.
