Did you know that most corals contain symbiotic algae called zooxanthellae in their gastrodermal cells? I bet you don't know. The coral also provides the algae with a protected environment and the compounds necessary for photosynthesis.



Zooxanthellae often are critical elements in the continuing health of reef-building corals. When the zooxanthellae are expelled, the colony takes on a stark white appearance, which is commonly described as “coral bleaching”.