One of the big threats to coral is the rising temperature of the oceans. Although corals have been around for millions of years, they are fragile animals in some ways, particularly when it comes to changes in temperature. Here is what happens: there are organisms called zooxanthellae (pronounced zoo-uh-zan-thel-ee), which are very small and live inside most of the shallow-water corals. These zooxanthellae can carry out photosynthesis; in other words, they can turn sunlight into food. They are so efficient at producing food from sunlight that they can feed themselves and feed the coral as well. Therefore, the main source of food and energy for these corals to grow comes from the zooxanthellae that live inside them. In return, corals protect the zooxanthellae and provide some nutrients to help them grow. This very friendly relationship between coral and zooxanthellae is known as mutualism.

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