Zooxanthellae and Coral Bleaching

Tiny plant-like organisms called zooxanthellae live in the tissues of many animals, including some corals, anemones, and jellyfish, sponges, flatworms, mollusks and foraminifera. These microscopic algae capture sunlight and convert it into energy, just like plants, to provide essential nutrients to the corals. In exchange, they have a place to live inside the animal's body. But when the zooxanthellae are under stress, such as high temperatures, they will die or leave their host—a process known as bleaching.

Close-up photograph of translucent coral polyps, showing the symbiotic algae living inside.
What is coral? The answer is coral is an animal. This cutaway diagram of a coral polyp shows the location of its photosynthetic algae, or zooxanthellae, which coral needs to survive.Flower-like clusters of pink polyps make up this coral colony.Compare the healthy coral on the left with the bleached coral on the right.These bleached corals in the Gulf of Mexico are the result of increased water temperatures.A photo of coral visibly affected by disease. An underwater photo of coral recovering from a bleaching event.