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Corals: builders of the reef

Corals are remarkable animals, capable of creating vast structures. Watch the video to enter their extraordinary world. Witness them feeding, admire their forms and colours, and find out about their intriguing reproduction.

Corals are living colonies of tiny tube-like animals called polyps - the individuals of some species are just 3mm long. Each polyp has a mouth surrounded by tentacles, usually arranged with six-fold symmetry.

The polyps produce a hard outer skeleton made of calcium carbonate, each laying down a hexagon-shaped foundation. This grows by up to 10 centimetres a year and the coral develops into various shapes and sizes, depending on the species.

Together with coralline algae and other groups that produce limestone skeletons, corals gradually build up the complex three-dimensional structure of a reef.

This habitable architecture is more than just colourful underwater scenery. In fact, it provides shelter and food for a quarter of all marine life. It also protects millions of people living in coastal communities as well as mangrove and seagrass environments (which are important nursery habitats for fish) by diffusing wave energy by up to 97 per cent.