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), by sedimentation caused by human activities, and by increasing and recurring coral bleaching due to climate change. Although the Australian government declared the reef a marine sanctuary in 1975, a 2012 study estimated that half of the coral had disappeared since 1985, with losses much greater in some areas than others. High water temperatures in 2016–17 and 2020 damaged large areas of coral.
A 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. Known to Australian aborigines for thousands of years, the reef was discovered by the Western world when Capt. James Cook's ship ran aground there in 1770; it was explored in the 19th cent. by Matthew Flinders and Charles Darwin.
See R. Endean, Australia's Great Barrier Reef (1983); I. McCalman, The Reef: A Passionate History (2014).
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