The growing calcium carbonate framework of coral creates habitats for other organisms. Brilliantly colored invertebrates and fish find their niches in the coral reef, along the sandy bottom of the sheltered lagoon, in the deep water of the outer reef, or anywhere in between.
The reef-building corals depend on photosynthetic algae, or zooxanthellae (zo-zan-THELL-lee), that live inside their tissues. These organisms produce food and oxygen that corals use to grow. In turn, the corals release waste products that the zooxanthellae use during photosynthesis. Through this mutually beneficial relationship, the coral and algae are able to exchange energy and important gases with each other. The exact nature of this relationship is not completely understood, but without algae the reef-building corals could not secrete their massive skeletons.