A coral island or series of coral islands forming a ring that nearly or entirely encloses a shallow lagoon. Atolls are surrounded by deep ocean water and range in diameter from about 1 km (0.62 mi) to over 100 km (62 mi). They are especially common in the western and central Pacific Ocean and serve as important habitats for corals, algae and fishes.

Modified from atoll. (n.d.) The American Heritage® Science Dictionary. (2005). Retrieved August 26 2014 from

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