There are many organisms other than
fish that live in the coral reef. There are starfish, seahorses,
polyps, plankton, sponges, sea
cucumbers, and countless numbers of others.
"The polyps that build the
reefs are known as stony corals. They live together in colonies.
Cells on the outside of the polyps' bodies collect a chemical called
calcium carbonate from the sea water. Calcium carbonate hardens to
form limestone, and this grows into a protective shell around each
polyp. When the polyps die, their shells remain. As new
polyps grow on the old limestone shells, the reef becomes larger."