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In exchange, the coral provides the algae with shelter.

Some corals build stony skeletons around themselves and are called hard corals. Others grow wood-like cores for support and are called soft corals (like the one shown here). Soft corals are flexible and often resemble plants or trees.

Corals are animals, related to jellyfish. These flower-like clusters are the living part of the coral, called polyps. Polyps can live on their own, but when they find a suitable home, they divide into many thousands of identical clones. The polyps connect to one another, creating a colony that acts as a single organism.

This species of coral lives in deeper water. It can’t get its food from algae like the shallow water species do, because there isn’t enough sunlight. Instead, the polyps have a mouth surrounded by a ring of tentacles, which help them trap food, just like their jellyfish cousins.

In this case, the blue colour is made by the coral itself.

Corals can be found in tropical ocean waters around the world, and they come in every colour of the rainbow. But did you know that many shallow water coral species are actually translucent? They get their wild pop of colour from photosynthetic algae (called zooxanthellae) which live inside the coral. The algae turn sunlight into nutrients, which the coral can eat.

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3This pink coral (called a sea fan) provides the perfect camouflage for three pygmy seahorses. Many species which live on coral have evolved vivid colours to help them blend in with the reef.

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Coral reefs occupy less than 1% of the ocean floor but support nearly 25% of all marine species. A healthy reef is like a bustling city, teeming with fish and turtles, as well as shrimps, crabs, snails and squid.

The tiny fish shown here is called a goby. There are at least 2,000 different species of goby and more than half of them are found on coral reefs, where they can use the complex architecture of the reef to hide.

5Mushroom corals, like the one shown here, are unusual because they can move about freely as adults, relocating to other parts of the reef as they see fit. Young mushroom corals are attached to the reef by a stalk, but when they reach sufficient size, the stalk breaks and the mushroom coral then lives unattached with the mouth side up. If overturned, it can right itself again!

6Corals come is a wide variety of shapes and sizes. They can be as small as an egg or as large as a house! Some form flat table-like structures and some are round or ball-shaped. Staghorn coral looks like - you guessed it - the antlers of a stag, while the sea fan pictured here resembles the branching structure of a tree.

7Coral reefs are like living medicine cabinets. Because they can’t move about, corals (and the species that live on them) have developed a range of chemical defence mechanisms to keep them safe from predators. Some of these chemicals have been used to develop treatments against diseases like cancer, arthritis and Alzheimer’s - to name just a few!

8Because of global warming, ocean temperatures are rising. That may sound like a good thing for your next beach holiday, but corals don’t like it when the water gets too warm. Stressed corals lose their photosynthetic algae, which takes away their food source and their colour. This is called coral bleaching. Some corals can bounce back from bleaching events, if given a chance to recover. Scientists say it is important to slow down climate change so that coral reefs can remain healthy and colourful.

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