S P O T ／ SPOT-364

Ohirugi Mangrove Colony of Oike

大池のオヒルギ群落おおいけのおひるぎぐんらく

Mangroves are coastal trees. They live where the river meets the tide, roots braced in salt mud, the most boundary-bound plants on earth. So a forest of them growing around a freshwater lake in the dead center of an island, 360 kilometers from the nearest mainland and cut off from the sea entirely, is a small geological impossibility — which is exactly what you find at Oike on Minami Daito. The island itself is an oddity: an uplifted coral atoll far out in the Pacific, ringed by cliffs and dished in the middle like a saucer, its interior pocked with karst lakes formed where limestone simply dissolved. Oike is the largest of them, a sheet of fresh water nearly half a square kilometer wide. And around it grows Ohirugi, Bruguiera gymnorhiza — stranded here, the scientists believe, more than eight thousand years ago, when the reefs heaved up out of the sea and carried a strip of shoreline with them, locking the mangroves inland forever. They have grown in fresh water, away from the tide, ever since. Designated a National Natural Monument in 1975, the "landlocked Ohirugi" of Oike is one of the few places on the planet where you can watch a coastal forest survive in a place the coast left behind.