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Coral nutrition

Corals derive their food energy from three sources: plankton captured by their tentacles, organic nutrients absorbed directly from the water, and organic compounds provided by the zooxanthellae. For the reef-building corals, the latter is by far the most important.

In the presence of sunlight, the zooxanthellae produce oxygen and photosynthetically fix nutrients—glycerol, glucose and amino acids—which are "leaked" to the surrounding tissues of the coral polyp. The raw materials for this process are the waste products of the coral animal: carbon dioxide, ammonia, nitrates and phosphates. It is a very efficient, almost self-sustaining partnership.

— David Pickell

On the steep walls of Indonesian reefs, normally deep-dwelling species can be seen at relatively shallow depths. This is a male square-spot anthias, Pseudanthias pleurotaenia.

These are not the only forms, and scientists studying reef topography offer many more types. For example, bank reefs, reefs that grow up more or less in patches in open water where the depths are relatively shallow, are an important type in the Coral Sea off Australia. These reefs often form at the edge of undersea plates, and appear when geologic activity causes an uplifting of the bottom. If the bottom is pushed up high enough that sunlight can reach it, a bank reef will form.