This coral reef contains a variety of stony corals. This image was captured by NOAA photographer Julie Bedford in the waters off the coast of Fiji in the Pacific Ocean. Coral reefs are buils from tiny animals known as coral polyps. These tiny animals form massive colonies and secrete calcium carbonate to build hard, stony skeletons. Over thousands of years, the hard skeletons of dead coral builds up to form coral reefs. Only the outer layer of a reef is actually alive.