Commonly seen types include the brain, elkhorn, staghorn, star and pillar corals. As coral polyps develop, they produce calcium carbonate. The excretion of this mineral by thousands of polyps, over hundreds of years, results in the large, hard reef structures that we see today. The colonies of soft corals, called gorgonians, contain more protein than minerals, and thus they can be seen swaying in the currents. Common soft corals in the Florida Keys include sea fans, whips, plumes and rods.
Coral polyps are basically colorless.
One type of algae is especially important to coral growth. Living a symbiotic existence within the actual tissue of the polyps are zooxanthellae. These microscopic plant cells convert sunlight into energy, giving off oxygen that nourishes their coral hosts. The polyps, in turn, provide protection and nutrition to support the zooxanthallae. All corals are fragile, and require a very specific aquatic environment in which to live.