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The Great Barrier Reef in Australia is the world's largest coral reef system, composed of roughly 3,000 individual reefs and 900 islands stretching for 2,600 kilometres (1,616 mi) over an area of approximately 344,400 square kilometres (132,974 sq mi). The reef is located in the Coral Sea, off the coast of Queensland in northeast Australia.
The Great Barrier Reef can be seen from outer space and is the world's biggest single structure made by living organisms. This reef structure is composed of and built by billions of tiny organisms, known as coral polyps. The Great Barrier Reef supports a wide diversity of life, and was selected as a World Heritage Site in 1981. CNN has labelled it one of the seven natural wonders of the world. The Queensland National Trust has named it a state icon of Queensland.
A large part of the reef is protected by the Great Barrier Reef Marine Park, which helps to limit the impact of human use, such as overfishing and tourism. Other environmental pressures to the reef and its ecosystem include water quality from runoff, climate change accompanied by mass coral bleaching, and cyclic outbreaks of the crown-of-thorns starfish.
The most significant threat to the Great Barrier Reef is climate change. Mass coral bleaching events due to rising ocean temperatures occurred in of the summers of 1998, 2002 and 2006, and coral bleaching will likely become an annual occurrence. A draft report by the UN Intergovernmental Panel on Climate Change states that the Great Barrier Reef is at grave risk and will be "functionally extinct" by 2030. Climate change has implications for other forms of life on the Great Barrier Reef as well - some fish's preferred temperature range lead them to seek new areas to live, thus causing chick mortality in seabirds that prey on the fish. Climate change will also affect the population and available habitat of sea turtles.
Another key threat faced by the Great Barrier Reef is pollution and declining water quality. The rivers of north eastern Australia provide significant pollution of the Reef during tropical flood events with over 90% of this pollution being sourced from farms. Farm run-off is polluted as a result of overgrazing and excessive fertiliser and pesticide use. Due to the range of human uses made of the water catchment area adjacent to the Great Barrier Reef, water quality has declined owing to the sediment and chemical runoff from farming, and to loss of coastal wetlands which are a natural filter. It is thought that the mechanism behind poor water quality affecting the reefs is due to increased light and oxygen competition from algae.
The crown-of-thorns starfish is a coral reef predator which preys on coral polyps. Large outbreaks of these starfish can devastate reefs. In 2000, an outbreak contributed to a loss of 66% of live coral cover on sampled reefs in a study by the CRC Reefs Research Centre. Outbreaks are believed to occur in natural cycles, exacerbated by poor water quality and overfishing of the starfish's predators.
The unsustainable overfishing of keystone species, such as the Giant Triton, can cause disruption to food chains vital to life on the reef. Fishing also impacts the reef through increased pollution from boats, by-catch of unwanted species (such as dolphins and turtles) and reef habitat destruction from trawling, anchors and nets. As of the middle of 2004, approximately one-third of the Great Barrier Reef Marine Park is protected from species removal of any kind, including fishing, without written permission.
Other threats to the Great Barrier Reef include shipping accidents, oil spills, and tropical cyclones. Wikipedia |
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