Coral reefs are "constructional physiographic features of tropical seas consisting fundamentally of a rigid calcareous framework made up mainly of the interlocked and encrusting skeletons of reef-building (hermatypic) corals (Wells,1957). The principal organisms responsible for the construction of modern day coral reefs, the stony corals, comprise the cnidarian order Scleractinia, which is closely allied to the sea anemones (Actinaria). Individual polyps secrete a calcium carbonate skeletal cup (calyx) beneath the basal epidermis. In most coral species the polyps remain connected by living tissue forming a colony and calcium carbonate is deposited beneath the basal epidermis of the entire colony, thereby constructing a three-dimensional mass of calcium carbonate which increases in size with the passage of time. The living tissues of reef building corals are packed with unicellular symbiotic dinoflagellates termed zooxanthellae which have been shown to be of Importance in both the calcification of the skeleton and in production of organic material on the reef.