Great Barrier Reef

The Great Barrier Reef is the world's largest coral reef. The reef is located in the Coral Sea off the coast of Queensland in north-east Australia. It stretches over 2000 kilometres in length and can be seen from space. An ancient barrier reef similar to the Great Barrier Reef can be found in The Kimberlies.

Environmental threats

The Great Barrier Reef is a large system of about 900 islands and over 3000 coral reefs, which mostly lie some distance from the mainland coastline. The coastline of north eastern Australia has no major rivers, except during tropical flood events caused by cyclones (hurricanes), several major urban centres with Cairns http://www.cityofcairns.qld.gov.au/, Townsville http://www.townsvilleonline.com.au/, Mackay http://www.mackayholidays.info/, Rockhampton http://www.sunzine.net/rockhampton/rcity.htm and the industrial city of Gladstone http://www.sunzine.net/gladstone/welcome.html. Cairns and Townsville are the largest of these coastal cities with populations of approximately 150,000 each http://www.oesr.qld.gov.au/. Unlike most reef environments the Great Barrier Reef is the only one where the catchment area is home to industrialised urban areas and where extensive areas of coastal lands and rangelands have been used for agricultural and pastoral purposes.

Related Topics:
Cairns - Townsville - Mackay - Rockhampton - Gladstone

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Due to the range of human uses made of the catchment adjacent to the Great Barrier Reef some 400 of the 3000 reefs are within a risk zone where water quality has declined owing to sediment and chemical runoff from farming, and to loss of coastal wetlands which are a natural filter. Principal agricultural activity is sugar cane in the wet tropics and cattle grazing in the dry tropics regions. Both are considered significant factors affecting water quality.

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The most significant threat to the future of the Great Barrier Reef in its current form and of the planet's other tropical reef ecosystems is global warming. Many of the corals of the Great Barrier Reef are currently living at the upper edge of their temperature tolerance, as demonstrated in the coral bleaching events of the summers of 1998 and 2002. Under the stress of waters that remain too warm for too long, corals expel their photosynthesizing zooxanthellae and turn colourless, revealing their white skeletons, and if the water does not cool within about a month the coral dies.

Related Topics:
Ecosystem - Global warming - Coral bleaching - 1998 - 2002 - Zooxanthella

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Global warming has triggered the collapse of reef ecosystems throughout the tropics. Increased global temperatures bring more violent tropical storms, but reef systems are naturally resilient and recover from storm battering. With an upward trend in temperature apparently continuing, much more coral bleaching is expected to occur in the coming decades.

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Crown-of-Thorns starfish are natural predators of corals. They have a life cycle with many eggs released annually, that enables this species to boom-and-bust like locusts in a desert. The cycles are thought to be enhanced by declines in water quality such as excess nutrients from farm runoff. Since scientists and other users of the reef have been able to observe crown-of-thorns outbreaks, about 1/3 of the entire system has been affected since the 1960s. The link to an animation of Crown-of-Thorns starfish outbreaks illustrates, using data collected from the Australian Institute of Marine Science Long Term Monitoring Program, the occurrence of Crown-of-Thorns starfish outbreaks http://www.aims.gov.au/monmap/cotsanimation/cots.htm.

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