Coral polyps eat tiny single-celled algae called zooxanthellae, which live within the coral's tissue. These tiny algae are plants that use sunlight in the photosynthetic process, thereby requiring that corals grow in clear, shallow water, where the sun can reach them. The zooxanthellae give coral its color. You can learn about the role of sunlight and carbon dioxide in photosynthesis in the Biology Gateways activities, The Role of Light in Photosynthesis and Fueling Photosynthesis with Carbon Dioxide and Water . The Role of Coral Reefs Reefs serve as home not only to live polyps but also to many species of algae, seaweed, sponge, and mollusks.
Coral reefs provide a barrier for coastal areas by breaking the waves of severe storms.
They help prevent coastal erosion, flooding, and the loss of property along the shore. Many coastal communities also benefit from the tourism and fishing generated by coral reefs. Like tropical rainforests, the rich biodiversity of the coral reef ecosystem may serve as a source for unique chemicals with medicinal properties, just waiting to be explored and discovered. Coral itself can be used in human bone grafts. Sponges growing on reefs can provide virus-fighting agents.