into the blue

SEYCHELLES'S LESSER-VISITED OUTER ISLANDS HAVE BECOME AN ECO-TOURISM PARADISE. STEPHANIE RAFANELLI DIVES IN

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In an abandoned copra plantation on Astove, a tiny atoll in Seychelles, I find giant tortoises.

Beneath the palm trees they look like the helmets of a hiding army platoon. The land, the domain too of hermit crabs and fallen coconuts, is littered with shells. It encircles eight square miles of lagoon, forming a thin border between sky and ocean. Migratory birds make it their landing strip; green turtles use it as a nesting ground, plowing tracks through sand as powdery as snow. Though Astove’s sand flats are as smooth as mother-of-pearl, its reefs are treacherous. Sharp blades of fossilized coral, or champignon, can shred feet and destroy vessels. A ghost yacht, the Shangri-La, lies beached on the atoll’s northwestern shore; no one knows its past. Astove is also surrounded by the tempestuous waters of the western Indian Ocean—the former Sea of Zanj, feared by medieval Arab explorers—that, whipped up by the trade winds, roll and roar in the summer. Windswept isolation, inhospitality to humans, and piracy have historically kept this place one of the planet’s truly wild and naturally protected places. That's the reason I'm here.

Beneath the water's mercury surface, I snorkel through Astove's oyster-shaped reef and find tiny fish twitching electrically like particles in a grainy film as well as giant specimens gliding en masse through bars of light. Battalions of bluestripe snapper and humphead wrasse—just two of the thousand species that swim here—jump in unison with the current before a vertical coral garden. The reef wall has a drop of 3,000 feet; with half a mile of blackness beneath me, I might appear to be floating in space. When I come up for air, the lava lamp glow of sunset makes me feel that I am indeed drifting on some fringe of the earth.