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Just beneath the waves in shallow tropical seas you'll find a world teeming with life. It's here that we find coral reefs - colourful habitats where countless creatures live.

Unfortunately like many habitats, coral reefs are struggling with the changing climates and environments we see today. These changes lead to 'coral bleaching'.

What is 'coral bleaching'?

Animals have evolved over millions of years to live within the environment that they find themselves in. When that environment changes too quickly, they find it difficult to adapt in time to surive.

Higher temperatures and warmer oceans, among other things, put the coral under stress. This causes the zooxanthellae to be expelled (thrown out) by the coral, a process known as bleaching.

coral polyp diagram

Much of the colour of the living tissues of a coral comes from the zooxanthellae within. Once the zooxanthellae are gone, the tissues are almost transparent and the white colour of the coral's stoney skeleton shows through.

This coral is still alive but at great risk without the food that the zooxanthellae provide. Left too long like this, the coral polyps will die. However, researchers are finding that if temperatures drop again, corals can regain the zooxanthellae from the surrounding water.

Discover more about what zooxanthellae is, and about corals in our Nature Classroom post here.

How to make a reef spinner

  • You'll need; paper, string, colours, glue.
  • Follow the instructions on the activity sheet, cutting around the edge of your chosen reef.
  • Create a vibrant reef on one side only, using whichever materials you like best. Paint, collage, pencils or crayons; it just needs to be as colourful as coral reefs can be.
  • Now turn over your reefs, stretch a piece of string across the middle of the lower one and fold the upper reef down. Sealing the string on the inside.
  • Twirl the string between your fingers and watch your reef lose and regain its colour.

Dive further into a reef with more crafts and messy summer makes in Crafty Creatures: Dive into a Coral Reef