The Great Barrier Reef is the world's largest coral reef. It stretches for 2,600 kilometres (1,616 mi) in the Coral Sea along the Northeast coast of Queensland, covering an area of approximately 300,000 square kilometres. 'It contains the world's largest collection of coral reefs, with 400 types of coral, 1,500 species of fish and 4,000 types of mollusc'*. The diversity of species is equalled only by that of the rainforests. However, human  activities in the Reef, as in the rainforests, have caused a drastic decline in this wonder of nature. For this reason in 1975 the Great Barrier Reef   Marine Park was brought into being by the Australian government for the purpose of preserving the area's outstanding biodiversity whilst allowing for reasonable use. 1981 the Great Barrier Reef was inscribed on the World Heritage List.

Reef building Corals thrive in clear, shallow, coastal, waters of tropical seas. The various reefs and cays are the basis for the great variety of sea  and animal life in the Coral Reef. Coral animals basically consist of polyps, which secrete a hard, circular corallite (made of calcium carbonate).  This circular corallite forms numerous radiating walls, which become the hard shell we recognize as coral. The coral animal continues living and producing its secretions in the uppermost part of the corallite. Reef building corals live in symbiosis with a single-celled micro algae (zooxanthellae), which provides them with food by photosynthesis, while the coral polyp provides the algae with nutrients in the form of their excrements. Thus  these corals grow much faster than non-symbiotic corals. The colour of coral results from the photosynthesis of the algae. Generally, healthy coral  has deep colour and becomes light when unhealthy. Coral colonies create most imaginative structures...