Coral Reefs:

There are two different types of coral, hard coral and soft coral.  Soft coral do not make reefs, but hard coral do.  An animal called a coral polyp forms coral reefs.  The coral polyp has a soft inside and a hard outside made of limestone.  The polyps live in groups and when they die, they leave behind their hard shell.  Over a long period of time the hard shells form a reef.  It takes thousands of years for a reef to form.
         Coral reefs are found in warm shallow water near land.  They are found in tropical waters where the temperature is between 70 and 85 degrees Fahrenheit.  Most coral reefs are found in the Pacific Ocean near Africa, Australia and India.  There are also reefs found near the southern United States and in the Caribbean.  The map below shows where coral reefs are located.

         There are three different kinds of coral reefs.  There are fringing reefs, barrier reefs, and coral atolls.  Fringing reefs form along coastlines.  They are found in shallow water.  Barrier reefs are found farther out in the water.  They grow parallel to the shore and are separated from land by a body of water called a lagoon.  The Great Barrier Reef near Australia is the biggest reef in the world at over 1,257 miles long.  The last type of reef is a coral atoll.  It is formed when coral grows on top of old volcanoes that are sunk in the ocean.  They actually start out as fringe reefs when the volcano is an island, but when the volcano sinks, only the reef is left.

picture of a coral polyp

Pictures drawn by Dylan