Great Barrier Reef, largest complex of coral reef in the world, c.1,250 mi (2,000 km) long, in the Coral Sea, forming a natural breakwater for the coast of Queensland, NE Australia. Composed of more than 2,800 individual reefs, the Great Barrier Reef is separated from the mainland by a shallow lagoon from 10 to 100 mi (16–161 km) wide. In some places it is more than 400 ft (122 m) thick. The coral in the reef is threatened, however, by predation by the crown-of-thorns starfish, by damage caused by cyclones (hurricanes), and by coral bleaching; a 2012 study estimated that half of the coral had disappeared since 1985, although the losses were much greater in some areas than others.
major tourist attraction, the reef has many islets, coral gardens, and unusual marine life. The Great Barrier Reef Marine Park, more than 130,000 sq mi (340,000 sq km), encompasses most of the reefs and interreefal areas as well as the neighboring lagoon and a large section of the continental shelf. It is the largest UNESCO World Heritage Area.
See R. Endean, Australia's Great Barrier Reef (1983).