Coral Reefs

Coral reefs are beautiful structures that grow on the oceans bottom. They are sometimes refered to as sea gardens. The are composed of coral skeletons that build up on other coral skeletons. Corals are tiny sea organisms that live in colonies of several individuals. Coral reefs usually grow in tropical seas in an area known as the photic zone, an area of water that receives a large amount of sunlight for photosynthesis to occur. This zone also has mild wave action that occurs (waves that are not strong enough to destroy the reef). There has to be some wave action occur to be able to stir up the water enough to circulate oxygen and food around. There are several different forms a reef can take on. An apron reef is one that is short and slopes down from a peninsular shore. A fringing reef is directly attached to a shore. A barrier reef is one that is seperated from the mainland by a deep lagoon. Reefs alos cover about 284,300 sq. Km'sof the worlds oceans and support a large amount of biodiversity. Corals live in a very nutrient poor enviroment, but a process of nutrient cycling between the reef, zooxanthellae and and other organisms associated with the reef provide the right environment to be so rich in biodiversity.
Although reefs are such a beautiful environment, rich in biodiversity, they are being threatened, with activity being human activity being the primary threat. Humans continue to over-fish and pollute the worlds oceans, which causes a serious threat to the oceans ecosystems. But one thing that humans are doing to help save these ecosystems is putting them as marine protected areas.

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~ http://en.wikipedia.org/wiki/Coral_reef