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 of a Coral Polyp
The brownish-green specks are the zooxanthellae that most shallow, warm-water corals depend on for much of their food.
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Where Do They Live?
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.
Photo Collection of Dr. James P. McVey, NOAA Sea Grant Program
Bleached Corals, Pacific Ocean
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 taken at a reef near Bocas del Toro, Panama. The reef suffered a mass bleaching event in the summer of 2010, when water temperatures were unusually high. In this photo, healthy brown coral gives way to the frontlines of disease.
These corals are still in recovery after a mass bleaching in Panama, in the summer of 2010. You can see some bleaching on the tops, but the sides are looking good.