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Iriomote Ishigaki NP, Okinawa
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In Yaeyama, distant storm waves once made reef caves boom like warning bells. On Ishigaki, people watched named formations 午の方ピー and 新川ユーニ for signs of rain or fair weather.
The reef’s food story reaches Yaeyama kitchens: coral habitats support irabucha (parrotfish), eeguwa (fusiliers) and mibai (groupers)—fish that help sustain local fishers and appear on regional tables.
Some reef corals once had household jobs: mushroom-shaped kusabiraishi and manjūishi were used to grate tubers and ginger, while rounded brain coral could serve as a house’s foundation stone.
More than 360 reef-building coral species have been recorded in the Yaeyama waters that include Sekisei Lagoon—over 80% of the 420–430 species known from Japan, despite this being near the reefs’ northern range.
Yaeyama’s white coral sand was once spread in gardens and schoolyards for more than its looks: it made paths easier to see at night and helped people spot a habu snake approaching.
Reef-dwelling suijigai and kumogai shells were once hung at Yaeyama doorways as charms against illness and evil spirits. Their pointed projections were thought to help keep unwanted visitors out.
Sekisei Lagoon may help supply coral larvae to reefs farther north: it lies at the southern end of the Ryukyu Islands, beside the north-flowing Kuroshio. Japan’s Environment Ministry also recognizes the reef as an important larval source.
Many Japanese reefs fringe island shores, but Sekisei’s waters are relatively deep—about 10–20 m—and support reefs closer to a barrier-reef form. The Ministry of the Environment lists it as an important example of this reef type.
“Sekisei” combines 石 from Ishigaki and 西 from Iriomote. Geographer Tsuyoshi Tamura proposed the name in 1966; although widely used for the reef sea between the islands, the name has no single formally defined boundary.
After 2 typhoons in September 2022, warm surface water may have mixed with cooler deep water. Average coral bleaching fell from 92.8% that September to 50.2% in December, though average live-coral cover also fell.
In an early restoration project, small seafloor holders collected naturally spawned coral larvae; after about 1½ years, young corals were fixed to reef rock. The trial placed 18 restoration units around Kuroshima.
Sekisei Lagoon’s first restoration council began in 2006 with 89 participants: 32 individuals, 30 organizations, 20 local public bodies and 7 national agencies. Fishers, tourism and diving operators, researchers and officials all had a place.
In the 1970s, crown-of-thorns starfish erupted across Sekisei Lagoon and devastated its coral, despite major control efforts. Their numbers later declined, and coral communities began recovering in the early 1990s—before later bleaching events struck.
The long-term restoration vision is to recover the rich reef ecosystem seen when the area became a national park in 1972. The plan records local recollections that back then it was hard to find a place without coral.
A 2025 study measured phosphorus stored in Sekisei’s limestone seabed—not just in moving seawater. Sites with more stored phosphorus tended to have fewer corals and more bleaching, offering a new way to investigate land-based impacts.
