Reef FactsThe world's first coral reefs occurred about 500 million years ago, and the first close relatives of modern corals developed in southern Europe about 230 million years ago. By comparison, the Great Barrier Reef is relatively young at just 500,000 years old. The current reef's structure is much younger at less than around 8,000 years old. Most modern reefs have formed on hard surfaces in the ocean, such as a base of an old reef that died during a period when sea level was lower, or the edge of a rocky island. Depending on how they start out, several types of reefs can form. Some coral reefs form in the deep ocean and are called atolls. The theories on how coral reefs form were first put forward by Charles Darwin (of The Origin of Species fame) who proposed that atolls form around the edges of high volcanic islands that gradually submerge beneath the sea with changes in sea level or subsidence of the land. Thus an atoll starts life as a fringing reef, then becomes more of a ring growing on the shrinking land-mass, until the land disappears and just the coral circle remains. In some cases, the coral growth is unable to keep pace with the sinking island, and sunken dead reefs have been found.
external image barrier.jpgHabitat: Coral reefs are found in shallow water, ranging to depths of 60 m. Some species prefer either cooler temperate water while others are found along tropical reefs, such as the Great Barrier Reef, with waters ranging in temperatures from 18 - 33 °C.
Living in colonies: They generally occur in large numbers as colonies of individual polyps linked by tissue. Resources, such as food, are then shared amongst the individuals in the colony.
Coral Size: Individual polyps range from 3 - 56 mm in diameter or height; while colony size varies from 75 mm -1500 mm (1.5 m) in width, height or length.
Some corals have a mutualistic relationship with algae called zooxanthellae. A mutualistic relationship is one where both parties benefit from their partnership. The algae use sunlight and the polyp’s waste products to make oxygen and food. These substances leak into the surrounding tissues of the polyp and can provide up to 98% of the polyp’s dietary requirements. These corals are found in shallow water, as they require sunlight to survive. They are generally fawn, brown or green in colour, due to the yellow-brown colour of the zooxanthellae.

Endangered Great Barrier Reef Overview
The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching
File:Map of Great Barrier Reef Demis.png
File:Map of Great Barrier Reef Demis.png
for over 2,600 kilometres (1,600 mi) over an area of approximately 344,400 square kilometres (133,000 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 7 natural wonders of the world.
Great Barrier Reef endangered
International Australia, home of the Great Barrier Reef, is the last nation on Earth that you'd expect to be knowingly destroying coral habitats. But that's just what will happen if the state of Queensland approves an expansion in shale oil operations -- unless you help stop them. Coral reefs around the world are suffering from climate change. As the climate heats up so do the oceans, causing the organisms that give coral its colour and food to die. Climate change is mostly caused by burning fossil fuels such as oil, coal and gas. Studies show that without a significant reduction in fossil fuel emissions coral reefs could disappear in less than 100 years. An example of this problem is Australia's world famous Great Barrier Reef, which lies off the state of Queensland. At around 2000 kilometres long it is the world's largest reef. But unless projected levels of climate change are slowed, much of the reef will be dead in decades. Last year the reef experienced its worst ever case of coral bleaching, with over 60 per cent being affected.

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