The coral reef is a barrier of corals, it is found near the coasts or around the islands, its structure is the hard skeleton of tiny animals called corals or polyps.
Colonies of polyps form on rocks in shallow waters of the oceans, when some die, others are born on top of them.
After many years coral islands can arise because of the millions and millions of polyps skeletons.
Coral reefs are places where thousands of beautiful colored fish live, the shallow waters protect them from enemies, like sharks and there they can get enough food to eat, some fish bite the coral cover and eat the polyp.
In Australia there is the largest expanse of coral reef, one thousand five hundred kilometers long, where some three hundred and forty species of coral have been found.
Image source: http://whyquantumphysicists.com/did-you-know-you-are-a-walking-coral-reef/