Great Nicobar is the largest and southernmost island in the Nicobar group, itself the southern extension of the Andaman and Nicobar archipelago that trails from Myanmar into the Bay of Bengal. Galathea National Park occupies the island's southern tip, separated from the larger Campbell Bay National Park to the north by a 12-kilometer forest buffer zone. Together they form the core of the Great Nicobar Biosphere Reserve, recognized by UNESCO in 2013. The park's geography is defined by its isolation. Port Blair, the territorial capital on another island 470 kilometers to the north, is the nearest city of any consequence. Flights from Chennai or Kolkata take roughly two hours to reach Port Blair; from there, reaching Great Nicobar requires further travel by sea or helicopter. This remoteness has been the park's greatest protection -- and, paradoxically, the reason its ecosystems remain so intact.

Galathea's climate is relentlessly tropical. There is no winter here -- only heat, humidity, and monsoons that dump between 3,000 and 3,800 millimeters of rain annually. The result is dense tropical and subtropical moist broadleaf forest, canopy unbroken, undergrowth thick enough to discourage casual exploration. The park's vegetation is considered among the best-preserved tropical rainforest in the world, a distinction owed largely to the fact that almost no one lives nearby to cut it down. Endemism runs high. Geographic isolation from both mainland Asia and the rest of the archipelago has allowed species to evolve along their own paths. Plants and animals found here exist nowhere else -- a biological treasury locked away on an island most people have never heard of.

Three species define Galathea's wildlife spectacle. The giant robber crab -- also called the coconut crab -- is the largest land-living arthropod on Earth, capable of cracking coconuts with its claws. It thrives in the park's coastal forests. The Nicobar megapode, a ground-nesting bird that incubates its eggs in mounds of decaying vegetation rather than sitting on them, inhabits the forest floor. And the Nicobar pigeon, iridescent and heavy-bodied, moves through the canopy in flocks. But the most dramatic visitor is seasonal. From February through December, leatherback sea turtles -- the largest turtles in the world, reaching weights of over 500 kilograms -- crawl onto Galathea Bay's beaches to lay their eggs. These same beaches and the turtles that depend on them are now at the center of a fierce conservation debate.

India's Great Nicobar Development Plan proposes transforming this thousand-square-kilometer island into a military and commercial hub. The $9 billion project includes an international container transshipment port in Galathea Bay, the upgrade of Campbell Bay's airstrip to a dual-use military-civilian airport, a gas and solar power plant, and a greenfield township designed to house hundreds of thousands of people. The strategic logic is straightforward: Great Nicobar commands the western approach to the Strait of Malacca, one of the world's busiest shipping lanes, and India wants a permanent presence there. The ecological cost is less straightforward. The proposed port sits in Galathea Bay, precisely where the leatherback turtles nest. Construction at the scale envisioned would fragment the biosphere reserve and industrialize an island whose primary value, to this point, has been its wildness. The park was gazetted in 1992 to protect what the Danish surveyors found remarkable a century and a half earlier. Whether that protection will survive the century ahead is an open question -- one that pits national security against biological heritage on a remote island where, for now, the crabs and turtles still outnumber the people.