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The Great Barrier Reef is the world's largest system of coral reefs, mangrove and estuarine environments, and the Great Barrier Reef Marine Park covers an area of about 348 700 km².

The Great Barrier Reef is a chain of coral reefs about 2 300 km long, skirting the continental shelf off the coast of Queensland, Australia, stretching from just south of the Tropic of Capricorn, towards the coastal waters of Papua New Guinea. It extends from below sea level to 40 m above sea level, and is 72 km wide at its widest point. It has about 3 400 individual coral reefs separated by deep water channels, including 760 fringing reefs (1 to over 10 000 hectares) of various shapes. There are approximately 300 coral cays, including 213 unvegetated cays, 43 vegetated cays, 44 low wooded islands, and 618 continental islands. The islands include Lizard, Green, Fitzroy, Frankland, Dunk and Hinchinbrook. Some of the islands have a substructure of igneous rocks, mainly granite or volcanics.

The Reef comprises 400 different species of coral, 4000 different species of mollusc, and many other kinds of invertebrates. There are 500 species of seaweed, 16 species of sea snake, 1500 species of fish, and 215 bird species, plus dugong and sea turtles. Individual reefs are of two main types: platform reefs formed from radial growths, and wall reefs resulting from elongated growths, often in areas of strong water currents. There are also fringing reefs on sub-tidal rock of the main coastline or continental islands. Each reef has a thin layer of living coral capping a structure made up mainly of calcareous sand and rubble from the breakdown and consolidation of coral and other skeletal material. Many of the present reef areas were once hills on a former coastal plain, and these became islands when the water level rose after the last Ice Age, to be colonised by coral polyps. Each coral polyp lives inside a shell of aragonite (calcium carbonate), and the shells of dead coral are eventually cemented together and covered with more calcium carbonate, from encrusting calcareous algae. The polyps can only grow in shallow warm water, less than about 30 m depth and water temperatures above about 18° C.

At the Great Barrier Reef the Australian Museum operates the

a world-leading supplier of on-reef facilities for coral reef research and education.