Coral reef is the mass of corals build up by accumulation of skeletons of coral polyps and other marine organisms.
The following are 3 types of coral reefs.
- Fringing reefs – this is platform of corals attached to coastline and extending seaward for distance of few hundred meters. The surface of the reef is highly irregular with much broken corals and many large hollows resulting from selective solution; however the inner lagoon is absent or weakly developed. Fringing reef grow near coastline around island or continents. They are separated from the shores by shallow and narrow lagoons. Example of fringing reef can be found along the coast of East Africa from Somalia to Mozambique.
- Barrier reef – this is large coral reef running parallel to the coastline, from which it is separated by deep and deep lagoon. The most famous example of barrier reef is Great Barrier Reef of Eastern Australia, which extend for for over 2000 kilometers. Barrier reef is massive and complex structure, comprising an outer line of coral reef, innumerable cays and larger island laying some 50 – 200 kilometers off shore, together with many inner reefs.
- Atoll – this is the coral reef surrounding a central lagoon, commonly found among the island of Southern Pacific. It is believed that atoll has been formed above former island; as these submerged either as the result of subsidence of sea floor or rise of sea level, these submerged island provided the base for coral growth which grew seaward and outward to form atoll.