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Updated: July 29, 2013 17:47 IST

Underwater empire

K. R. VISALAKSHI
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An aerial view: Off Australia's Queensland state.
AP
An aerial view: Off Australia's Queensland state.

Though they are so minute, the polyp and the plant have forged a relationship that has become a natural wonder.

The Great Barrier Reef stretching 1,300 miles along the North Eastern coast of Australia is a brilliantly coloured under-water kingdom. Millions of tiny coral polyps have created this mighty and colourful kingdom, which has withstood the force of the lashing waves for several centuries.

How was it made?

Less than half an inch long, the coral polyp is a close relative of jelly fish and sea anemones. It has a cylindrical body and a round disc on the top, with a row of stinging tentacles. The opening at the centre of the disc is the mouth. Any prey brushing against the tentacles get paralysed. It is swiftly drawn into the mouth and digested.

As the polyp matures, it secretes limestone to form a protective casing called corallum. Each polyp splits into identical polyps, which remain in contact with the parent, till they can form their own protective casings. The older polyps die and are covered by the corallum of their offspring. Thus extensive colonies of the polyps linked by the limestone casings are soon formed.

Only coral polyps living in the shallow and warm water can create coral reef. These polyps maintain a “symbiotic” relationship with algae called zooxanthellae. Any relationship between two or more different organisms in close association which benefits all the organisms involved is called a “symbiotic relationship”.

These single celled microscopic algae live inside the coral, probably helping its host with an increased supply of oxygen and faster waste disposal system.

With the help of “the guest” algae, the polyps can grow 10 times faster, than without it. Polyps need algae and the algae need sunlight to survive. So the most flourishing reefs are found between 15 feet and 90 feet under water. Rarely any coral is seen below the depth of 180 feet.

Isn’t it amazing that a tiny creature (less than half-an-inch in length) and a microscopic plant (invisible to human eye) have formed a successful relationship and given rise to the most colourful and impenetrable barrier under water.

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Illustration: Sreejith R. Kumar

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