The algae and coral reef relationship is best described as:
Reef-building corals live in an intimate nutritional mutualism with intracellular dinoflagellates of the family Symbiodiniaceae, commonly called zooxanthellae. The algae photosynthesize and transfer a substantial fraction of fixed carbon to the coral host, supporting respiration, growth, and rapid calcium-carbonate deposition in nutrient-poor tropical water. Corals supply carbon dioxide, nitrogenous wastes, phosphorus, and a protected, well-lit cellular habitat. This reciprocal metabolic exchange explains the high productivity of reefs despite low surrounding nutrient concentrations. Many reef
Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 8-13
