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Coral reefs house an array of species such as coral polyps, tropical fish, shellfish, turtles and various sea plants. About 25 percent of the global reef systems have been destroyed by human activities and about another 60 percent are threatened on some level. The Great Barrier Reef, off the coast of Queensland, is the world's largest natural reef system. Although it is protected as a World Heritage Area, it is still greatly impacted by the human environment. Pollution, mining and tourism all have detrimental effects on coral reefs. The Great Barrier Reef is most vulnerable to pollution from urban and agricultural run-off.

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Water quality: Pollution and waste dumping

In order to flourish, coral reefs require clear, salty water that is low in nutrients such as phosphorous and nitrogen. Pollution from the land is entering rivers and streams and is carried to the oceans. There are many different rivers that flow into the lagoon areas of the Great Barrier Reef. The polluted water from rivers on Australia's west coast, and from around the world, is changing the condition of the ocean in the Great Barrier Reef region.

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Currently, about 80 percent of the material dumped at sea is dredged material. Dredged material is dirt, sand and mud (sediment). Sediment has been eroded from land as a result of agriculture, urban development and deforestation. This sediment enters rivers and streams and is carried to the oceans. Sediment also enters the oceans through the natural process of erosion. The influx of sediment into the Great Barrier Reef region is blocking the clear waters. This makes the water cloudy, and it is then difficult for the zooxanthellae algae to undergo photosynthesis. If the algae cannot undergo photosynthesis, they will die. This will also cause the coral polyps to die since they rely on the algae to survive.

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Other material dumped at sea includes metals, glass, plastics, wood, chemicals and nuclear waste. It is estimated that about seven billion tonnes of litter is put into the oceans every year. Over half of this is in various forms of plastic. Plastics, and other materials, can take several decades to decompose. Every year, about one million seabirds around the world die as a result of plastics. Plastics that are dumped into the oceans are circulated to other parts of the world through global currents. The plastics and various other materials are building up and harming not only the Great Barrier Reef but ocean ecosystems around the world.

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Agriculture is also affecting the water condition of the oceans and the Great Barrier Reef region. Even though agricultural practices take place on the land, the cycle of water throughout the global environment causes problems for the reef ecosystem. Currently, about 80 percent of the land along the coast of the reef is used for cattle grazing and crop growing. Various pesticides, chemicals and fertilisers are often used on crops. Farming animals produces a lot of waste. These pollutants enter streams and river through surface run-off or soil infiltration. The rivers and streams then end in the ocean. Chemicals and pesticides are poisonous and can kill various life forms on the reef. Fertilisers and animal waste are high in phosphorous and nitrogen. These two nutrients are deadly to coral polyps.

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Tourism impacts

Tourism has both negative and positive effects on the Great Barrier Reef. Tourism helps generate revenue for local communities and for the upkeep of the Marine Park. Tourism can also help spread awareness about the importance of the delicate ecosystem of the reef. Tourism, however, can also have negative impacts on the natural reef environment. With more people in one area, the demand for natural resources increases. This can result in the overuse of natural resources as well as producing more waste and pollution. It is also hard to monitor the actions of tourists at all times. Some tourists do not obey the rules and damage the coral reef. The importance of tourism and its impact on the Great Barrier Reef is discussed in further detail in Chapter 4.

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Non-native species

Non-native species, also known as introduced species, are plants and animals that do not naturally live in the Great Barrier Reef. These species have been transported by humans, generally on ships, from another region of the world. Various fish, molluscs, worms, plants, algae, diseases and viruses have been transported to the Great Barrier Reef. It is estimated that over 250 different species have been introduced into Australian waters from various parts of the world. Many of these are becoming pests. Diseases and viruses are contaminating seafood. Some introduced species are predators that eat native fish. If dense populations of non-native species are established in Australian waters and especially the Great Barrier Reef, the natural ecosystem may be destroyed.

Climate changes

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A current climate change issue is global warming. The increase of greenhouse gases within the atmosphere is a result of an increase in carbon emissions from rapid urban development. The build-up of greenhouse gases within the environment is causing global temperatures to rise. This is also causing ocean temperatures to rise. Coral polyps, the key component of a coral reef, require a stable climate. Changes in water conditions in the Great Barrier Reef as a result of global warming and pollution have caused coral bleaching. Coral bleaching occurs when the zooxanthallae algae and the coral polyps die as a result of environmental changes. It is possible for coral to recover from this if the environmental changes are not too severe and do not last for long. If global temperatures continue to rise, however, the coral polyps will not be able to recover from coral bleaching.


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