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.
Threats
Climate change
The Great Barrier Reef Marine Park Authority considers the greatest threat to the Great Barrier Reef to be climate change, causing ocean warming which increases coral bleaching. Mass coral bleaching events due to elevated ocean temperatures occurred in the summers of 1998, 2002 and 2006, and coral bleaching is expected to become an annual occurrence. Climate change has implications for other forms of reef life—some fish's preferred temperature range leads them to seek new habitat, thus increasing chick mortality in predatory seabirds. Climate change will also affect the population and sea turtle's available habitat.
Pollution
Another key threat faced by the Great Barrier Reef is pollution and declining water quality. The rivers of north eastern Australia pollute the Reef during tropical flood events. Over 90% of this pollution comes from farm runoff. Farm run-off is caused byovergrazing, excessive fertiliser use, and pesticide use.
The runoff problem is exacerbated by the loss of coastal wetlands which act as a natural filter for toxins and help deposit sediment. It is thought that the poor water quality is due to increased light and oxygen competition from algae.
Another key threat faced by the Great Barrier Reef is pollution and declining water quality. The rivers of north eastern Australia pollute the Reef during tropical flood events. Over 90% of this pollution comes from farm runoff. Farm run-off is caused byovergrazing, excessive fertiliser use, and pesticide use.
The runoff problem is exacerbated by the loss of coastal wetlands which act as a natural filter for toxins and help deposit sediment. It is thought that the poor water quality is due to increased light and oxygen competition from algae.