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Yambaru NP, Okinawa
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At about 10 hectares, Gesashi is Okinawa Island’s largest mangrove forest. The Ryukyu Government protected it in 1959; on May 15, 1972, it became a national natural monument.
Three mangrove species grow here, but one gives Gesashi a special botanical distinction: the Yaeyama mangrove reaches its northern natural limit at the Gesashi River.
Look for 3 different root shapes: Yaeyama mangroves brace themselves on stilt-like roots, O-hirugi send up knee-shaped roots, and Me-hirugi spread flat, board-like roots.
Some hirugi seeds begin sprouting while still attached to the parent tree. When they fall, the seedlings may float with the tide or lodge in the mud—a remarkable, built-in planting strategy.
At Gesashi, the male Okinawa hakusen shio-maneki fiddler crab waves its oversized white claw to attract a mate. The motion looks like a little fan dance; “hakusen” means “white fan.”
A study recorded 55 fish species in Gesashi River’s mangrove waters during 2000–2002. Comparing 4 Okinawan island sites, researchers found fish species numbers increased farther south.
A 2014 prefectural survey documented 63 species of decapod crustaceans—crabs, prawns, and relatives—in the Gesashi mangroves, spanning 23 families.
Local memories recorded in an Environment Ministry storybook tell of children walking along Gesashi River by moonlight to catch shrimp. The river was part of their childhood playground.
In 1993, Higashi chose hirugi—the mangrove tree—as its official village tree, marking the community’s 70th anniversary. Its namesake forest grows at the mouth of Gesashi River.
Red soil and sediment filled small channels inside the forest, pushing wet habitat toward dry land. Since FY2015, Okinawa Prefecture’s restoration work has included clearing buried channels.
Gesashi has local “rangers”: Higashi-certified guides who monitor environmental changes and introduced species, helping protect the mangroves while guiding visitors.
