The great Barrier reef, stretching 1300 miles long along the North Eastern coast of Australia, is a brilliantly coloured under water kingdom. Crores of tiny coral polyps have created this mighty and colourful kingdom, which has withstood the force of the lashing waves for several centuries.

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 gets paralyzed. 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 off springs. 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”.

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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 ten times faster, than without the help of “the guest”.

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 colorful and impenetrable barrier under water!

Visalakshi Ramani