Coconut crab mysteries revealed

Crews bound for the South Pacific and points west always seem especially curious about the legendary coconut crab (Birgus latro, family Coenobitidae). They’re actually no more than oversized land hermit crabs that choose to abandon their shell at a tender age. Prized as a traditional food throughout the Pacific islands, these slow-growing, long-lived invertebrates have become severely depleted over much of their range. We’ve only seen them on sparsely populated, uninhabited, or protected islets and islands.

Juveniles emerge from aquatic larval development and adopt a shell, typical of hermit crabs. Unlike other hermits, they permanently abandon the shell as they become adults, move farther inland and construct a burrow. They emerge at night to feed omnivorously on a variety of fresh and decaying matter, including, as their name suggests, coconuts. To this end, these crabs scale towering coconut palms by using the spike-like ends of their legs for purchase. One sure sign of an inhabited abode — a burrow, log or some abandoned structure like World War II-era gun revetments on Pacific islands — is the presence of shredded coconut husks around the entrance.

This was the clue that led us to our first coconut crab, in the company of then-island manager Roger Lextrait on otherwise uninhabited Palmyra Atoll, the northernmost of the Line Islands. Lextrait ducked into the low concrete bunker and scrabbled loudly, making indecipherable exclamations in French. I was just about to start dragging him out by the legs, assuming the crab had him by the nose, when he squirmed back with a triumphant grin, grasping a hefty, purplish-gray specimen, and dropped it into a burlap sack. Lextrait, a retired chef, later prepared a sumptuous meal featuring the sweet, delicate meat of the unfortunate crab.

The truth is, however, coconut crab populations are in trouble. Modern-day Indo-Pacific seafarers should not kill and consume these animals, other than for survival emergencies, unless the meal is offered by an island host. A species with this life history simply can’t sustain heavy collecting pressure, and we shouldn’t compete with the locals for something they need to leave alone themselves for a while. Like sea turtles and giant clams, coconut crabs need time to recover. Voyaging sailors can help immeasurably by just saying no.

By Ocean Navigator