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The dangers of coral bleaching

By Evelyn Kay, Year 7


Did you know that coral reefs cover 1% of the ocean, but they are home to over a quarter of all known marine species! They are known for their bright colours and exotic shapes, but there is more to these wonderful corals that meets the eye.


Coral reefs are built by tiny animals called polyps, which are related to jellyfish. They have simple bodies consisting of little more than a stalk containing a stomach with a ring of tentacles on top surrounding the mouth. These polyps attach to rock on the sea floor, then starts dividing and forms a colony.



These coral polyps build walls of calcium carbonate to protect their soft bodies from hungry predators. Eventually, they become huge stony structures, each species creating its own architectural form.

Over a very long time, they build up into great reefs. The largest of them all, is ‘The Great Barrier Reef’ of north eastern Australia, it is also visible from space.


Surprisingly, the colours of the corals do not come from the polyps themselves, but from the algae living inside their them. These work together with the polyps to transform warm shallow seas, poor in nutrients, into an oasis of life. But it is one that hangs in the balance!


Coral bleaching generally happens when the corals become stressed and eject their algae, exposing the bone white of their calcium carbonate skeletons. Without their algae, the polyps get smallers, and seaweed begins to take over!

This smothers the coral skeletons and the reef then turns, with alarming speed, from wonderland to wasteland.


Coral reefs are extremely sensitive, this is shown when coral bleaching occurs due to a change in temperature from 1 degree. Even a small difference like this can create a devastating impact on the oceans eco-systems.


Coral reefs, such as the ‘Red Sea’ in Egypt, are among the most biodiverse habitats on earth. Yet, while they are rich and complex eco-systems, they are also fragile.

At the current rate of climate change, some predict that 90% of the world’s coral reefs could disappear within decades as the oceans become warmer and more acidic.

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