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Corals and Coral Reefs

Biology | 10-13 yrs | Interactive, Learning Pod

Wouldn’t it be funny if all your bones were outside your skin? This is actually something that does indeed exist. It is known as an exoskeleton and not the endo-skeleton that it is now.

What are Corals?

Animals that we see around us have endo-skeletons while some life forms like cockroaches and crabs have exo-skeletons. Corals too wear their bones on the outside of their body. For a long time, people were not sure if corals were plants or animals. But seeing it has a skeleton, it can be classified as an animal. The skeleton is at the base of the organism and the soft body contracts into it when it is attacked.

What is a Coral Reef?

Corals live in colonies, in shallow warm waters of oceans. Corals are beautiful and colorful, but they lose their color if there are changes in the temperature of the water. A single organism is less than .02 inches in size. Colonies of these exo-skeletons are known as a reef.

Like any other animal, corals are made of thin-walled cells, as opposed to the thick-walled plant cell. The corals that we see in pictures or around us are polyps. Each polyp is a blob of flesh and is actually a group of many ‘creatures,’ all identical like twins. Corals have radial symmetry – like a pizza, they can be cut into identical segments of a circle. Each of these organisms has a mouth at the centre, surrounded by tentacles. Food is ingested and waste is expelled from the same central mouth.

What do Corals eat?

They have a gastro-vascular system, a much more primitive version of the human digestive system. Food that is ingested is shared among the organisms in the polyp. Corals release a chemical that immobilizes their prey. Then they ingest it and the stomach closes. It reopens after digestion and the waste is expelled. Corals feed on plankton, small fish and even small particles of dead organic matter.

Corals multiply in reefs. All corals release eggs and sperm at the same time, the same way that fish spawn their eggs in the water. When the eggs and sperm meet, tens of thousands of new corals are formed. Sometimes a single polyp may just grow a new organism on its own or it may split and become two. This also helps to increase the coral population.

Activity –

Study a few pictures of corals and see if you can spot –
(a) a polyp
(b) the radial symmetry in each organism.

More Information –

Click here to know more about the Great Barrier Reef, the largest living structure in the world.