Coral reefs are among the most diverse communities on this planet, often described as
"rainforests of the sea". Reefs occur in clear, shallow waters throughout tropical regions
across the globe. Formed by the calcium carbonate skeletons, the backbone of the reef is
built by tiny coral animals that make up large coral colonies. Coralline algae produce calcium
carbonate, which cements the coral skeletons together, forming the continuous reef
structure. The skeletons of tube worms, mollusks, and other organisms also become
incorporated into the reef.          

Scientific Classification - Corals are part of a group of organisms called Cnidarians.  This
group includes jellyfish, sea anemones, and sea fans
and reef-building corals.

The reef-building corals can be identified by their stony skeletons made of calcium
carbonate.  A coral colony consists of thousands of individual coral animals, each similar in
appearance to a small sea anemone with its base attached to a calcareous cup. Corals are
armed with a ring of tentacles used to capture zooplankton from the surrounding water.
Reef-building corals also contain symbiotic algae, called zooxanthellae, within their tissues.
These single-cell algae have a mutualistic association with the coral hosts, a relationship
that benefits both partners. The algae utilize carbon dioxide and nitrogen-based waste
products released from the coral. In return, the algae perform photosynthesis, producing
sugars and amino acids. These products are transported to the coral in support of its
nutritional needs.
Coral Reefs
Florida Keys National Marine Sanctuary