coral reef summary

Written and fact-checked by The Editors of Encyclopaedia Britannica

Below is the article summary. For the full article, see coral reef.

coral reef, Ridge or hummock formed in shallow ocean areas from the external skeletons of corals. The skeleton consists of calcium carbonate (CaCO₃), or limestone. A coral reef may grow into a permanent coral island, or it may take one of four principal forms. Fringing reefs consist of a flat reef area around a nonreef island. Barrier reefs may lie a mile or more offshore, separated from the landmass by a lagoon or channel. Atolls are circular reefs without a central landmass. Patch reefs have irregular tablelike or pinnacle features. Smaller patches occur inside atoll lagoons; larger patches occur as isolated parts of any of the other three reef categories, and they sometimes occur completely separate from other kinds of reefs.

Great Barrier Reef Summary

Great Barrier Reef, complex of coral reefs, shoals, and islets in the Pacific Ocean off the northeastern coast of Australia that is the longest and largest reef complex in the world. The Great Barrier Reef extends in roughly a northwest-southeast direction for more than 1,250 miles (2,000 km), at

James D. Dana Summary

James D. Dana was an American geologist, mineralogist, and naturalist who, in explorations of the South Pacific, the U.S. Northwest, Europe, and elsewhere, made important studies of mountain building, volcanic activity, sea life, and the origin and structure of continents and ocean basins. Dana

Charles Darwin Summary

Charles Darwin was an English naturalist whose scientific theory of evolution by natural selection became the foundation of modern evolutionary studies. An affable country gentleman, Darwin at first shocked religious Victorian society by suggesting that animals and humans shared a common ancestry.

atoll Summary

Atoll, coral reef enclosing a lagoon. Atolls consist of ribbons of reef that may not always be circular but whose broad configuration is a closed shape up to dozens of kilometres across, enclosing a lagoon that may be approximately 50 metres (160 feet) deep or more. Most of the reef itself is a