Types Of Coral Reefs
Corals are small marine animals that secrete calcium carbonate exoskeleton for their protection. These calcium carbonate shells remain intact even when the animal dies out. Since these animals live in colonies these hard exoskeletons accumulate to form much a larger structure which is known as the coral reef.
Today after thousands of years of accumulation coral reefs are called as one of the most diverse ecosystems on the earth as within these reefs reside 25% of the sea animals including small fishes, molluscs, sponges and echinoderms.
Ideally coral reefs grow in warm and agitated water and require sunlight for their growth; therefore most of the coral reefs flourish best near the shore line of the sea. However they do exist deep in the oceans but these coral reefs are small and are less observed as compared to the ones that grow in shallow waters.
The coral reefs that we see today took a thousand years of making as the coral reefs formation is an extremely slow and gradual process.
The reason for it is that a coral community can only build reefs if they secrete calcium carbonate than removed and since the wave currents and other biological factors tend to break the skeletal structures as soon as they are secreted by the organism the building of reef is a very gradual process.
Although all the types of coral reefs are composed of same materials and formed by a same process, they differ on the bases of their shapes and their sizes and also their locations.
On the bases of these criteria following are the types of coral reefs:
The barrier reefs grow parallel to the shore of an island and are separated form it by a deep lagoon.
They grow mostly along the outer edges of the continental shelves. These reefs unlike the atolls are discontinuous composites of many small reefs each of which is separated by a channel.
The Darwin theory of the formation of atolls can also be applied to the barrier reefs. Just like the atolls, according to Darwin, the barrier reefs started as the fringing reefs.
They started to develop much later then the atolls when the rising of sea level and subsiding of the land became a slow process. They too got detached from the shoreline and stated growing parallel to it separated by a deep lagoon
These reefs can extend up to 100 meters and in some cases even more. They are found mostly indo pacific and Caribbean oceans. The most famous barrier reef is the Great Barrier Reef of Australia.
The fringing reefs grow either very close to the shore or directly attached to it. It takes nearly 10000 years for a fringing reef to grow and they started thousand years ago in shallow waters near the shoreline.
As the sea level stared to rise and due th the movement of the land these reefs started to grow upward and outwards at a fast pace to stay close to the land.
It is believed thet the other two types of the coral reefs started to grow as fringing reefs and later became barrier and atoll reefs.
The fringing reefs are commonly found in the carribbean oceans and red sea. Since they are close to the shorelines they are susceptible to human activities and can be damaged due to pollution and agricultural development.
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Atolls are continuous horse shoe shaped or circular reefs that can extend up to 100 miles in diameter. These reefs surround a large, deep central lagoon with their best developed parts facing side where wave energy is the greatest.
Generally the atolls of today took nearly 30 million years to be built. According to Darwin these reefs were initially fringing reefs that grew on the shoreline of a volcanic island. As the sea level started to rise gradually these reefs started to slowly detach from the island and the land started to move and sink.
As they moved they became barrier reefs separated from the land by a deep lagoon. When the land eventually sank completely these reefs were left alone far away from the land enclosing a deep central lagoon and hence atolls were formed.
Today they are most commonly found in the indo pacific regions, almost 300 atolls have been found there. They are also common in the shores of southern Mexico and the coast of Belize.
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