Coral reefs are very diverse and all vary in their size, form and type. Different ones form depending on the availability of the substratum and any long-term changes in sea level, light level and wave action (Cesar, 2002).
Charles Darwin first identified the different types of reef in the early 1800’s. His original observations have now been studied further and there are four main types of reef that have been identified: fringing reefs, barrier reefs, atolls and patch reefs. Fringing reefs, figure 3, are the most common type of reef and can be found in the Red Sea (Boaden and Seed, 1985). They grow seawards and run parallel with the shoreline of an oceanic island. On the side nearest the land, there is a shallow reef flat.
Barrier reefs also run parallel to a shoreline but are separated by a large lagoon. Moving out towards the sea, the reef can drop to great depths. They can be formed from a collection of reefs, cays, islands and channels, for example the Great Barrier Reef. Figure 4 shows an image of a helicopter view over the Great Barrier reef, the many different reefs and channels can be seen. Atolls are rings of reef that circulate a lagoon, they are usually found in oceanic waters and the surrounding waters may be many kilometers deep (Deas and Deas, 2005).
Patch reefs are surrounded by sand and are small reefs that grow in shallow lagoons, behind barrier reefs or within an atoll (Boaden and Seed, 1985).
Video showing the diverse habitat of the Great Barrier Reef:
Figure 5. Video of the Great Barrier Reef. Courtesy of youtube.