Great Barrier Reef

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Satellite image of part of the Great Barrier Reef
Satellite image of part of the Great Barrier Reef

The Great Barrier Reef, located near Queensland, Australia, is the world's largest coral reef. It stretches for 2.300 kilometres in length. James Cook discovered it on 11 June 1770, because of damage under his ship. When the ship approached the reef the captain realised that his vessel could not travel over it and he then ran aground and finally sank.

[edit] Geology

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The Reef Research Centre, a Cooperative Research Centre, has found coral 'skeleton' deposits that date back half a million years.[1] Corals have been growing in the region for as long as 25 million years, but have not always formed coral reefs.[2]

Disagreements about the age of the Great Barrier Reef stem from how reefs grow and shrink as the sea level changes. They can increase in diameter from 1 to 2 centimetres per year, and grow upwards anywhere from 1 to 15 centimetres per year; however, they are limited to growing above a depth of 150 metres due to their need for sunlight, and cannot grow above sea level.[3]

According to the Great Barrier Reef Marine Park Authority, the current, living reef is believed to have begun growing on an older platform about 20,000 years ago.[2] The Australian Institute of Marine Science agrees, which places the beginning of the growth of the current reef at the time of the Last Glacial Maximum. At around that time, the sea level was 120 metres lower than it is today. The land that formed the base of the Great Barrier Reef was a coastal plain with some larger hills (some of which were themselves remainders of older reefs).[4]

Heron Island, a coral cay in the southern Great Barrier Reef.
Heron Island, a coral cay in the southern Great Barrier Reef.

From 20,000 years ago until 6,000 years ago, the sea level rose steadily. As it rose, the corals could grow higher on the hills of the coastal plain. By around 13,000 years ago the sea level was 60 metres lower than the present day, and corals began to grow around the hills of the coastal plain, which were, by then, continental islands. As the sea level rose further still, most of the continental islands were covered by water. The corals could then overgrow the hills, to form the present cays and reefs. Sea level on the Great Barrier Reef has not risen significantly in the last 6,000 years.[4]The CRC Reef Research Centre estimates the age of the present, living reef structure at 6,000 to 8,000 years old.[1]

The remains of an ancient barrier reef similar to the Great Barrier Reef can be found in The Kimberley, a northern region of Western Australia.[5]

The Great Barrier Reef World Heritage Area has been divided into 70 bioregions,[6] of which 30 are reef bioregions,[7] and 40 are non-reef bioregions.[8] In the northern part of the Great Barrier Reef, ribbon reefs and deltaic reefs have formed; these structures are not found in the rest of the Great Barrier Reef system.[1]

[edit] Species

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Giant Clam on the Great Barrier Reef
Giant Clam on the Great Barrier Reef

The Great Barrier Reef supports many kinds of life, including many vulnerable, endangered species and some which may only live on the Great Barrier Reef.[9] 30 species of whales, dolphins, and porpoises have been found in the Great Barrier Reef, including the Dwarf Minke Whale, Indo-Pacific Humpback Dolphin and the Humpback Whale. Large populations of dugongs live there. Six species of sea turtle come to the reef to breed – Green Sea Turtle, Leatherback Sea Turtle, Hawksbill turtle, Loggerhead Sea Turtle, Flatback Turtle and the Olive Ridley. 15 species of seagrass attract the dugongs and turtles. Over 200 species of birds (including 40 species of waterbirds) live on the Great Barrier Reef, including the White-bellied Sea Eagle and Roseate Tern. 5000 species of mollusc have been recorded on the Great Barrier Reef including the Giant Clam and various nudibranches and cone snails. 17 species of sea snake live on the Great Barrier Reef. More than 1500 species of fish live on the reef, including the Clownfish, Red Bass, Red-Throat Emperor, and several species of Snapper and Coral Trout. 400 species of corals, both hard corals and soft corals are found on the reef. 500 species of marine algae or seaweed live on the reef. The irukandji jellyfish also lives on the reef.[10][11]

[edit] References

  1. 1.0 1.1 1.2 CRC Reef Research Centre Ltd. What is the Great Barrier Reef?. Retrieved on 2006-05-28.
  2. 2.0 2.1 Great Barrier Reef Marine Park Authority (2006). Fact Sheet 1 - Reef Facts For Tour Guides - The Big Picture. Retrieved on 2006-12-02. (PDF)
  3. MSN Encarta (2006). Great Barrier Reef. Retrieved on 2006-12-11.
  4. 4.0 4.1 Tobin, Barry (1998, revised 2003). How the Great Barrier Reef was formed. Australian Institute of Marine Science. Retrieved on 2006-11-22.
  5. Western Australia's Department of Environment and Conservation (2007). The Devonian 'Great Barrier Reef'. Retrieved on 2007-03-12.
  6. Great Barrier Reef Marine Park Authority. Representative Areas in the Marine Park. Retrieved on 2007-03-23.
  7. Great Barrier Reef Marine Park Authority. Reef Bioregions of the Great Barrier Reef World Heritage Area. Retrieved on 2007-03-23.
  8. Great Barrier Reef Marine Park Authority. Non-Reef Bioregions of the Great Barrier Reef. Retrieved on 2007-03-23.
  9. CSIRO (2006). Snapshot of life deep in the Great Barrier Reef. Retrieved on 2007-03-13.
  10. CRC Reef Research Centre Ltd. REEF FACTS: Plants and Animals on the Great Barrier Reef. Retrieved on 2006-07-14.
  11. Great Barrier Reef Marine Park Authority. Fauna and Flora of the Great Barrier Reef World Heritage Area. Retrieved on 2006-11-24.