What is Coral reef?
[[File:Blue Linckia Starfish.JPG|thumb|250px|right|Some of the [[biodiversity]] of the [[Great Barrier Reef]], off [[Queensland]], [[Australia]].]] [[File:Coral atoll formation animation.gif|thumb|right|A fringing reef can take ten thousand years to form, and an atoll can take up to 30 million years<ref>[http://oceanservice.noaa.gov/education/kits/corals/media/supp_coral04a.html Animation of coral atoll formation] [[NOAA]] Ocean Education Service. Retrieved 9 January 2010.</ref>]] A '''coral reef''' is a large under[[water]] structure made of dead and living [[coral]]s. In most healthy reefs, stony corals are predominant. They are built from [[Colony (biology)|colonial]] [[polyp]]s from the [[phylum]] [[Cnidaria]] which secrete an [[exoskeleton]] of [[calcium carbonate]]. The reefs are formed in tropical [[Ocean|marine]] areas (30 degrees north and south of the [[equator]]) and between the tropics. The reef acts as the home of many [[tropics|tropical]] [[fish]] and other animals. Coral reefs systems are a major [[tourism]] attraction because of their beauty and color of the corals and their many associated animals. People look at them while [[snorkeling]] and [[diving]]. One example of a coral reef is in [[Malaysia]] at Pulau Tioman, off the State of Pahang. The most famous is the [[Great Barrier Reef]] off the East coast of [[Australia]]. == Formation == Most present-day coral reefs were formed after the last [[ice age]] when melting ice caused the [[sea level]] to rise and flood the [[Continental shelf|continental shelves]]. This means they are less than 10,000 years old. As coral reef communities were established on the shelves, they built reefs that grew upwards, keeping pace with the rise in sea level. Reefs that did not keep pace became ''drowned reefs'', covered by so much water that there was insufficient light for further survival.<ref>[http://www.eoearth.org/article/Coral_reef#Types_of_Coral_Reefs Coral reef] ''The Encyclopedia of Earth'', Updated February 27, 2009.</ref> Coral reefs are also foun