General Information

Great Barrier Reef is a magnificent chain of more than 2500 coral reefs and several small islands in the Coral Sea, just off the northeastern coast of Australia. Home to the largest deposit of coral in the world, the reef extends about 2000 km from a point near Mackay, Queensland, to the Torres Strait. This length is comparable to the Pacific Coast of the United States. Despite being a narrow formation, its area has been calculated to be approximately 204,800 sq km.

The Formation of the Reef Environment

The coral reef is a ridge or elevated part of a relatively shallow area of the sea floor. It is formed by a rocklike accumulation of calcareous (calcium-containing) exoskeletons of coral animals, calcareous red algae, and mollusks. Built up layer by layer by living corals growing on top of the skeletons of past generations, coral reefs grow upward at rates of 1 to 20 cm per year. Coral reefs are tropical, extending to about 30^o north and south of the equator and forming only where surface waters are always above 20^oC.

Coral reefs are ecosystems with well-defined structures. Their numerous microhabitats and the productivity of the reefs support a great diversity of marine life.

Vegetation & Wildlife

The Great Barrier Reef was built upon a shallow fringe of continental shelf in waters warm enough for the coral to flourish. The abundance of sea life on and around the Great Barrier Reef is extraordinary. Besides corals, other forms of invertebrate reef life including anemones, worms, snails, lobsters, crayfish, prawns, jellyfish, and giant clams are present in great numbers. The native vertebrates include a great number of sea birds and more than 1,500 species of saltwater fishes. Many of the small fishes have brilliant colors and unusual shapes. Although the animal life is varied, vegetation above the surface of the water is limited, consisting only of about 30 to 40 species.

Since the early 1960s, crown-of-thorns starfish have invaded parts of the reef. These animals feed on coral and can destroy large portions of a coral reef. Fortunately, the Australian government has made efforts to limit destruction of the coral.

History

Europeans first discovered the Great Barrier Reef in the 1770 through the explorations of Captain James Cook. His ship, the Endeavour, hit a reef 32-km from land. Investigation of the reef, begun by Cook, continued throughout the 19th century.

Today, the reef is contained within the Great Barrier Reef Marine Park, managed by the Great Barrier Reef Marine Park Authority, an organization of the Australian Government. Established in 1976, the Authority’s primary purpose is to protect this unique environment from outside influences through its education of the public and recommendations to the government.

Current Conditions

Coral Bleaching

Many coral reefs around the world have recently been affected by bleaching, which is caused by the coral’s loss of symbiotic zooxanthellae. Widespread bleaching incidents occurred over the three-year period from 1986 to 1988, in areas such as Hawaii, Fiji, and the entire length of the Great Barrier Reef.

Although the true cause of these widespread bleaching incidents is unknown pollution, global warming, and ultraviolet radiation have been suggested as suspects. Recently, research has pointed out a new culprit, indicating that the cause may be the unusually warm marine conditions. Temperatures above 29 degrees Celsius have been shown to cause stress in corals. These temperatures increase the rate of photosynthesis by the symbiotic zooxanthellae that give coral their colour. The increased photosynthesis creates high concentrations of toxins in the coral tissue, which may cause the polyps to expel the zooxanthellae. As a result, the coral appears bleached.

Most bleached corals have difficulty recovering; a reef can take years to recover, and subsequent bleaching incidents can make the difficult process impossible. In the end, all reef organisms could potentially lose their habitat because of these incidents.

Industry

The irregularities of the sea floor immediately surrounding the reef make commercial netting of fish difficult. Therefore, fishing is carried out on a limited basis, bringing $250 million to the nation annually. Laws concerning commercial exploitation also protect the abundant sea turtles that were once captured for food.

The pearl-shell and scallop collecting industries are still undertaken by some of the islanders to the north. The Great Barrier Reef's abundance of sea life is a major tourist attraction for Australia. As one of the world's great natural systems, the Great Barrier Reef supports an annual $1 billion tourist industry.