The ring-shaped coral islands called atolls are a defining feature of the South Pacific, put on magnificent display in the recent Disney-Pixar film Moana. Atolls are known for being convenient harbors almost by default, rich habitats for marine life, and the source of the famous stark line between blue-water and green-water regions that surrounds Pacific islands. Atolls are also extraordinarily rare outside of the South Pacific, which is curious, because neither coral nor islands are similarly restricted. Other warm regions should have their own atolls, but they almost always don’t. So the question is…where are the Caribbean atolls?
It turns out this is a fairly involved question.