Coral Reefs

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Coral is a type of calcareous rock made of the skeletons of minute sea organisms called polyps. Over time, many such skeletons build up and form reef structures.

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Polyps are minute sea organisms that extract calcium from sea water to build skeletons for protecting their bodies. About 2,500 species of coral polyps are known, and they usually live in colonies.

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When polyps die, their skeletons settle on the sea floor. New generations of polyps grow on top of the old skeletons, so layer after layer builds up. In time, a large mass of cemented skeletons forms …

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Coral polyps need warm water, generally between 20°C and 30°C, so coral reefs are found mainly between 30°N and 30°S latitudes. They also need sunlight, clear salt water, and suitable living condition…

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Coral polyps live at depths of 45 to 55 metres. This is because they need sufficient sunlight for growth.

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Polyps thrive well in clear salt water. Fresh water and highly saline water are harmful, and dirty water is also unsuitable. Coral growth needs clean marine conditions.

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River deposits are not favourable for polyps, so they avoid delta regions. Delicate coral growth is harmed by the muddy and deposited material brought by rivers.

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They need an adequate supply of oxygen and microscopic marine food called plankton. Food is more plentiful on the seaward side of a growing reef, so coral reefs grow faster on that side.