This algae lives within the tissue of the reef-building coral. The algae contributes to the calcification capability of corals by extracting carbon dioxide from the animal's body fluids. This increases the concentration of the carbonate ion needed for the precipitation of calcium carbonate. This relationship represents the interdependence of the system whereby both parties benefit. The coral contributes to the relationship by providing a supply of nutrients to the zooxanthella.
Corals host a variety of other organisms .
These massive formations also offer protection to a surprising assortment of fish, worms, snails and shellfish. Some fish benefit from the variety of cleaner shrimp and cleaner fish that set up cleaning stations on the coral reefs. These are an essential part of the well being of many larger fish on the reef due to the fact that they remove parasites and infectious tissue. This, of course, is added to the other major benefit that larger fish get from the reef, that being, the direct feeding on smaller prey. Some may only spawn during the lunar period.