Australia - Great Barrier Reef

Reef
Located in Pacific Ocean
Length 2,012 kilometers (1,250 miles)

The Great Barrier Reef is located in the Coral Sea off the northeast coast of Australia. Though its name suggests that it is a large single reef, it is actually a series of thousands of individual reefs and hundreds of small coral islands formed along the edge of the Queensland continental shelf. The Great Barrier Reef extends along the shelf edge and is the largest organic feature on Earth.

Coral reefs are formed by small animals that secrete a calcium carbonate skeleton. Millions of skeletons eventually form a reef. Unlike those, which form around oceanic islands due to subsidence, the Great Barrier Reef was caused by rising sea levels after last Ice Age. The corals contain algae in their tissue that require sunlight, making the reef grow upwards in response to rising sea levels. Corals also require warm seawater to thrive, probably near 25°C (77°F) and the Great Barrier Reef is ideally located in a region where the warm South Pacific Equatorial Current feeds into the East Australian Current. Although coral reefs appear to be rocky and indestructible, they are complex and fragile ecosystems.

Reefs Millions of Years in the Making
Parts of the Great Barrier Reef in Australia may be as much as 20 million years old. Most of the reef, however, has build up since the last Ice Age, over the pas 2,5 million years. The largest of its kind and one of the world's most impressive natural wonders, the reef extends south from Cape York Peninsula for 2,012 kilometers (about 1,250 miles). Conditions for coral growth are ideal, and the water is usually crystal clear. Red and blue-green algae near the surface give the reef a distinctive color. Although much of it is protected in national parks, increasing tourism, oil exploration, and limestone mining nonetheless threaten the reef.

Open Ocean
The Great Barrier Reef of Australia is the world's largest barrier reef. It comprises a system of coral reefs and islands that stretch more than 2,300 kilometers (about 1,430 miles) along Australia's eastern shore. An almost continuous line of breakers marks the location of the outer reefs, which line the rim of the continental shelf. Between the outer reefs and the beach are many crescent - or horseshoe-shaped inner reefs. The clear, warm, shallow waters of the Coral Sea provide ideal conditions for the corals and algae that make up the reef, and for the extraordinarily diverse marine life related to the reef system. The small islands that top some of the inner reefs are stabilized by vegetation growth. Many have been made national parks, and some of the reefs are marine national parks.

Scuba Diver on the Great Barrier Reef
The Great Barrier Reef stretches form more than 2,000 kilometers along the Queensland coast of Australia. It is the largest maritime park in the world. The numerous reefs and coral islands that make up the chain are home to a remarkable number of organism including starfish, sea turtles, sponges and more than 400 varieties of spectacularly colored coral. One of the best ways to see the fascinating marine life of the reef is to go scuba diving.

Sources:
Microsoft Encarta World Atlas 1998 Edition