Corals – architects of the underwater metropolis

Geetha Iyer

Coral These are times when the focus is on saving earth’s fast disappearing biodiversity. The diversity of life is the backbone of a biology course. This column introduces you to certain diverse life forms that are not often talked about in classrooms, but can be woven into the syllabus to provide absorbing and exciting lessons, subtly raising awareness for the need to conserve life forms without being pedantic.

I begin this Nature Watch series with Corals. Coral reefs are magnificent underwater empires, home to an estimated 25 per cent of all oceanic species. The reefs, with their spectacular colours and intricate patterns, are built by individual organisms called corals. These reefs provide shelter, nurseries, and homes to several exotic and diverse species thus earning the sobriquet of tropical rainforests (of the ocean). Like the rainforests these too are valuable resources and important constituents of earth’s ecosystems. To understand this metropolis under water, the buzzing mall, we need to first know about those organisms that construct these structures, namely, corals.

What are corals?
Corals are animals that belong to Phylum Cnidaria (the term Coelenterata is no longer valid and not used in International Conventions, though ICSE, CBSE and other school boards continue to use it). Whether small, free living individuals or large colonies, they all possess the same basic body plan – Coral polyps and Corallite. Each living coral is actually a coral polyp – a small, tiny animal. Some of them are capable of building a protective skeleton of calcium carbonate which is the corallite. When we say corals we generally refer to this, non-living part, the corallite or the calcium carbonate skeleton secreted around the living coral polyps for their protection. The intricate designs of the corals are nothing but the deposits of corallite. The corallite erode over time and are washed into the shore where they form the beaches.

The author is a consultant for science and environment education. She can be reached at

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