Most reef-building corals rely on partnerships with algae, or zooxanthellae, which live in their tissue. The coral serves as a home and provides products for photosynthesis, and in return the algae remove wastes and supply the coral with nutrients resulting from that photosynthesis. An added bonus is the algae giving corals their unique and beautiful colors! https://oceanservice.noaa.gov/education/tutorial_corals/coral02_zooxanthellae.html 📷: Noaa Fisheries/Damaris Torres-Puliza | NOAA Coral Re