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How are Coral Reefs, the Biggest Ecosystem, Formed?

Ningthoujam Sandhyarani May 10, 2019
Coral reefs are one of the oldest and largest living ecosystems on the Earth. This post includes some facts regarding their formation.
Coral reefs are large ecosystems formed by polyps, which secrete calcium carbonate. Around 1/4th of all the marine plants and animals are found in these underwater structures. With reference to this rich biodiversity, they are considered as the rain forests of the sea. Identified as the world's largest, the Great Barrier Reef, stretches about 2,600 Kms.

Where are Coral Reefs Formed?

Statistics reveal that coral reefs occupy only about 1 percent of the total surface area covered by oceans. Depending on their location, they are categorized under three primary types. The first and the most common type is fringing reef that remains attached to the shores, forming a border in the shoreline.
The second is the barrier reef, that also forms a border in the shoreline, but is not directly attached to the land mass. A deep lagoon separates the barrier reef and the mainland. The last type is atoll reef, which is a near circular reef with a lagoon in the center.

Formation of Coral Reefs

According to coral reef information, it is believed that the oldest reefs were formed approximately 500 million years back. The prerequisites for formation of these is warm temperature condition and sufficient sunlight.
This is the main reason why they are mostly found in shallow waters of the temperate and tropical oceans, where the average temperatures do not fall below 64 degrees F. Nevertheless, there are also deep water corals that can form them at greater depths of the ocean, under low light conditions.
If you go through the facts, you will find that the hard structure is nothing but the calcium carbonate (limestone) skeleton of the corals. Each colony houses numerous small, cylindrical polyps, which are connected with each other.
The reefs are formed exclusively by hard polyp, which forms a cup-shaped limestone skeleton around itself. Another type, known as soft polyp, does not secrete calcium carbonate as its skeleton. In short, soft polyps are not capable of forming them.
After the death of hard polyps, their skeleton serve as a new foundation for attachment of new polyps. The individual polyps are fragile, invertebrate animals having a column shaped body. The upper end bears tentacles, while the base is attached to the reef substrate.
During daytime, the polyps withdraw from the cup-shaped skeletons. The polyps live in symbiotic association with brown algae. The algae help in secretion of limestone and provide sugar to the polyps.
Formation of coral reefs is brought about by accumulation of death and living hard corals, under the influence of rising water levels in the marine biome. Since polyps are colonial species, they tend to grow and develop together. Consequently, skeleton growth takes place in masses.
As old polyps die, new polyps grow and the cycle continues. Over a span of time (thousands of years), and generation after generation, the skeletons accumulate extensively, leading to formation of stony structures, known as coral reefs. The uppermost portion contains live polyps.
It takes thousands of years for coral colonies to get established, which is quite a long time. Considering this, a major environmental issue is the natural and human threats to their existence. Thus, instant steps for saving coral reefs are crucial to conserve the oldest ecosystems of our planet.