There is a multitude of different kinds of coral on the Great Barrier Reef, including hundreds of species of both hexacorals (hard corals) and octocorals (sea pens, blue corals, soft corals and sea fans).
Hard corals can be further separated into two sub-groups. The zooxanthellate (reef-building or hermatypic) corals are ones that depend on zooxanthellae algae for nutrients. These shallow water corals have a major reef-building function. They are generally found in clear water less than 50 metres deep as the algae need light for photosynthesis.
The azooxanthellate (deep water or ahermatypic) corals do not contain zooxanthellae and therefore gain their nutrition solely from filtering plankton from seawater. These isolated, solitary or colonial forms rarely build big constructions and many of these coral species are present in non-reef environments in coastal areas such as Moreton Bay in Queensland.