What is the name of the symbiotic algae that lives inside coral?

The symbiotic algae that live inside coral are commonly called zooxanthellae. The term usually refers to microscopic, photosynthetic dinoflagellates living within the tissues of corals and other marine animals.

These partners perform photosynthesis and pass useful organic compounds—including sugars, glycerol, and amino acids—to the coral. In return, the algae receive carbon dioxide, nutrients, and a protected position close to sunlight. This partnership helps reef-building corals survive in nutrient-poor tropical waters and supplies much of the energy needed for growth and calcification.

“Zooxanthellae” is a familiar ecological term rather than the name of one single modern taxonomic group. Many coral symbionts once placed broadly in Symbiodinium have since been divided among several genera in the family Symbiodiniaceae. When heat, pollution, unusually strong light, or other stress damages the partnership, corals may expel the algae and turn white—a process called coral bleaching.