Figure 17.1 A mutualism between coral and zooxanthellae. A coral grabs food with its tentacles, which contain stinging cells, and pulls the food into its mouth. Zooxanthellae algae live along the surface of a coral’s tentacles where they obtain sunlight for photosynthesis. Corals provide a place for algae to live and emit CO2 that algae use in photosynthesis. As algae photosynthesize, they provide sugars and O2 that corals consume.