Revista de biología marina y oceanografía

Overview of Coral Reefs

Frank William Arnold

Corals consist of narrow layers or plates of calcium carbonate, also known as calcite or limestone. It is secreted by many soft-bodied animals known as Coral Polyps. Polyps have different size ranges; they may vary from a pinhead to a foot in length. Each polyp has a symbiotic relationship in which a host called zooxanthellae that gives coral its color. Zooxanthellae follow normal photosynthesis process and thus take in carbon dioxide and release oxygen and other essential nutrients which are used by the host polyp. The corals must be exposed to a sufficient amount of sunlight for their proper growth. In a nutshell, Coral Polyps may be defined as tiny, soft-bodied organisms that are related to jellyfish and sea anemones. Their base is composed of a hard and protective limestone skeleton known as calicle, which is responsible for the basic structure of coral reefs. When a polyp affixes itself to a rock on the seafloor, the formation of reefs begins which then divides into thousands of clones, thereby creating a colony that acts as a single organism. As colonies expand over the years, they join with other colonies and become reefs. Most of the coral reefs are made from stony corals, whose Polyps cluster in groups.