If it weren't for these primitive organisms none of what is out here today would be seen. The individual coral animal (Polyp) is usually only about 2-3mm in size, but most species form large colonies containing hundreds of polyps. Like other animals, corals need to obtain energy from an outside source - they can"t make food themselves. Therefore they have a microscopic algae (Zooxanthelle) living inside their tissues that photosynthesise. Producing oxygen and sugars for the coral to use. The coral obtains up to 90% of its energy from this algae, which enables it to build its calcium carbonate skeleton. It is this algae which gives the coral the majority of its brown or green colouring.
There are 400 different species of coral found across the Great Barrier Reef, most of which are hard, reef building corals. To make it easier to identify these corals, they are grouped into seven basic growth forms.
- Branching coral – are very fragile and are one of the faster growing species. They have much shorter on the reef flat than in deeper waters as they are exposed to more wave action.
- Encrusting coral – this form follows the contours of the reef.
- Columnar coral – corals that rise in columns. Often called knobbly coral on the reef flat because of its stunted bumpy appearance.
- Foliaceous coral – describes coral that resembles leaves. Includes blade coral, a fast growing species that provides hiding places for many small fish and crabs.
- Plate coral – a species not often found on the reef flat. It is fragile and designed to collect as much sunlight as possible. Quite often found in deeper areas of the reef slope where the light levels are lower.
- Massive (boulder) coral – looks like a boulder. A common species is brain coral (its experience speaks for itself).
- Mushroom coral – not often found on the reef flat. Unlike other species, this species is a free-living single polyp that can grow quite large.