Great Barrier Reef

a coral reef parallel to the coast of Queensland, in NE Australia. 1250 mi. (2010 km) long. Also called Barrier Reef.

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Long stretch of coral reef, shoals, and islets in the Pacific Ocean, off the northeastern coast of Queensland, Australia.

The largest deposit of coral in the world, it extends for more than 1,250 mi (2,000 km) along the Australian coast and has an area of some 135,000 sq mi (350,000 sq km). The reef has been formed over millions of years from the skeletons of a mass of living marine organisms. In addition to at least 300 species of hard coral, marine life includes anemones, worms, gastropods, lobsters, crayfishes, prawns, crabs, and a variety of fishes. Encrusting red algae form the purplish red algal rim that is one of the reef's characteristic features.

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▪ reef, Australia

 

complex of coral reefs (ocean), shoals, and islets in the Pacific Ocean off the northeastern coast of Australia. It extends in roughly a northwest-southeast direction for more than 1,250 miles (2,000 km), at an offshore distance ranging from 10 to 100 miles (16 to 160 km), and has an area of some 135,000 square miles (350,000 square km). It has been characterized, somewhat inaccurately, as the largest structure ever built by living creatures.

      The reef actually consists of some 2,100 individual reefs and some 800 fringing reefs (formed around islands or bordering coastlines). Many are dry or barely awash at low tide; some have islands of coral sand, or cays; others fringe high islands or the mainland coast. In spite of this variety, the reefs share a common origin: each has been formed, over millions of years, from the skeletons and skeletal waste of a mass of living marine organisms. The “bricks” in the reef framework are formed by the calcareous remains of the tiny creatures known as coral polyps (polyp) and hydrocorals, while the “cement” that binds these remains together is formed in large part by coralline algae and bryozoans (moss animal). The interstices of this framework have been filled in by vast quantities of skeletal waste produced by the pounding of the waves and the depredations of boring organisms.

      European exploration of the reef began in 1770, when the British explorer Captain James Cook (Cook, James) ran his ship aground on it. The work of charting channels and passages through the maze of reefs, begun by Cook, continued during the 19th century. The Great Barrier Reef Expedition of 1928–29 contributed important knowledge about coral physiology and the ecology of coral reefs. A modern laboratory on Heron Island continues scientific investigations, and several studies have been undertaken in other areas.

      The reef has risen on the shallow shelf fringing the Australian continent, in warm waters that have enabled the corals to flourish (they cannot exist where average temperatures fall below 70° F [21° C]). Borings have established that reefs were growing on the continental shelf as early as the Miocene Epoch (23.7 to 5.3 million years ago). Subsidence of the continental shelf has proceeded, with some reversals, since the early Miocene.

      The water environment of the Great Barrier Reef is formed by the surface water layer of the southwestern Pacific Ocean. The reef waters show little seasonal variation: surface-water temperature is high, ranging from 70° to 100° F (21° to 38° C). The waters are generally crystal-clear, with submarine features clearly visible at depths of 100 feet (30 metres).

      Forms of life include at least 300 species of hard coral as well as anemones (sea anemone), sponges (sponge), worms (worm), gastropods (gastropod), lobsters (lobster), crayfish, prawns (prawn), crabs (crab), and a great variety of fishes and birds. The most destructive reef animal is the crown-of-thorns starfish (Acanthaster planci), which has reduced the colour and attraction of many of the central reefs by eating much of the living coral. Encrusting red algae Lithothamnion and Porolithon form the fortifying purplish red algal rim that is one of the Great Barrier Reef's most characteristic features, while the green alga Halimeda flourishes almost everywhere. Above the surface, the plant life of the cays is very restricted, consisting of only some 30 to 40 species. Some varieties of mangrove occur in the northern cays.

      In addition to its scientific interest, the reef has become increasingly important as a tourist attraction. Growing concern over the preservation of its natural heritage has led to increased controls on such potentially threatening activities as drilling for petroleum resources. The extensive use of tourist craft and the sustainability of commercial fishing were controversial matters in the late 20th century.

      Supervision of the reef is largely the responsibility of the Great Barrier Reef Marine Park (declared in 1975), which encompasses the vast majority of the area. There are also smaller state and national parks. In 1981 the Great Barrier Reef was added to UNESCO's World Heritage List (World Heritage site), and the first comprehensive report on the state of the World Heritage area was produced in 1997.

Additional Reading

Isobel Bennett, The Great Barrier Reef (1971, reissued 1992); and Reader's Digest Visitors' Guide to the Great Barrier Reef (1988), provide overviews of the reef's ecosystem and include color photographs. Well-illustrated works on the flora and fauna are A.B. Cribb and J.W. Cribb, Plant Life of the Great Barrier Reef and Adjacent Shores (1985); and John E. Randall, Gerald R. Allen, and Roger C. Steene, Fishes of the Great Barrier Reef and Coral Sea, rev. and expanded ed. (1996). Neville Coleman, The Dive Sites of the Great Barrier Reef and the Coral Sea (1996), is a specialized guidebook with photos.

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