Coral Structure
Within the hexacorals, the order Scleractinia or true stony corals includes the majority of reef-building (hermatypic) corals. These are also known as hard corals, and lay down a skeleton by secreting calcium carbonate, a process known as calcification. Hermatypic Scleractinia corals have a good fossil record and can be traced back to the mid-Triassic over 200 million years ago. The EDGE coral reefs project focuses on these hermatypic Scleractinian corals.
The skeleton of an individual coral polyp is called a corallite, and it is variations in these structures that form the basis for species identification. These skeletons are critical to the formation of coral reefs. Growth rates for hermatypic corals can range from just a few millimetres to 15 cm per year. Hard corals grow into a diverse range of forms, known as life-forms, ranging from encrusting to branching, columnar, foliose (leaf-like), tabular (plate-like) and dome (also known as massive) structures. This morphology can be highly varied within coral species, as it is often influenced by environmental conditions, and so is of limited value for species identification but is useful for describing the more general topographical diversity of a reef. Large reef formations are built up by coral colonies over centuries or millennia and become highly complex and massive structures. For example the Great Barrier Reef in Australia is the largest biological structure in the world and is clearly visible from space.
