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Coral reefs are a part of the beautiful marine life setup that attracts scuba divers from all around the world. But what looks as a hard shell or rock which makes up the sides or the main part of an island are actually the exoskeletons of tiny marine animals known as Corals. Throughout their life they secrete calcium carbonate from their body which makes up their hard exoskeleton and provides a shelter and home to them. This exoskeleton becomes hard and rock-like once the coral dies; however new coral replaces the old one and keeps on building the coral colony. As the corals live in unison, the secretion of each unites to make these hard structures that we know as the coral reefs. Because the size of the corals is quite small therefore it can take thousands of years for the coral reef to increase in size that could make a difference.
There are three main types of coral reef though there are many other secondary forms. However according to Darwin’s theory of evolution, the three kinds of coral reefs are only different stages of its evolution and are not entirely distinct in kind. The following description of types of co
ral reef is also based on Darwin’s theory which is still regarded in studies of these colonies.
Fringing Coral Reef
Fringing Coral Reef is the first stage of building of coral reefs according to Darwin and hence is the first in the types of coral reef. Coral reefs started building on mostly the volcanic islands. It starts to build along the shore in the shallow water where there is ample sunlight. Thus the hard coral started to grow in favorable conditions. The fringing reef gives the appearance of outlining the borders of an island. But due to the glacial meltdown the levels of the seas began to rise and the islands started to subside; which brings us to the next type of coral reef.
Barrier Reef
As the island started to subside, the hard coral reef kept on growing on its own in those favorable environments. These no longer needed the support of the island to grow and kept on building up on the support of the older dead one. So unlike the fringing coral reefs, these types of coral reef were some kilometers away from the shore. One can see an island top in the middle and a band of barrier reef encircling it far away like The Great Barrier Reef in Australia which lies around 300 – 1000 meters away from the shore and is remarkably 2000 km in length. However it is not necessary for the reef to appear in complete circles; there could be broken patches in between.
Atolls
When the island in the center completely subsided, it resulted in the encircling atoll in which the coral continues to grow and maintain itself on the sea level forming a lagoon in between. The atolls have shown a remarkable ability to keep up with the changing sea levels. One of the best examples of these types of coral reef is the Carteret Atoll.