Coral atoll

High altitude aerial of Pacific coral island atollsReefs are the largest living structures in the world and the work of animals scarcely visible to the naked eye. Built on the slopes around the exposed peak of an underwater mountain, layer upon layer of coral skeletons accumulate, building a reef that can surround the island enclosing a lagoon.

Coral animals play a great role by enlarging an island, consolidating its presence.
The tentacles and mouths of polyps by the million strain the food from the sea, and secrete hard calcareous skeletons below and around themselves. Side by side and linked by flimsy tissues, they sit in tiny hollows into which they can withdraw, and in a concerted effort they build the magnificent edifice of a coral reef.

If the sea level rises, or the seamount subsides, the island may sink from sight leaving only an atoll - a ring of coral. It may seem little more than a beach alone in an ocean, but it is a living memorial to the vanished island.

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