Tropical Isle

Eight atolls in the Pacific represent the world’s largest marine protected area — the Phoenix Islands Protected Area. Atolls are low ring-shaped islands of coral rubble that form over millennia as coral reefs grow around volcanic islands that sink, leaving the coral ring exposed. A classic atoll, Nikumaroro has coconut palms ringing a warm, shallow central lagoon that is a nursery for young reef fish.

(Photo by Larry Madin, Woods Hole Oceanographic Institution)