Do you know that there is a little-known organism that plays a huge role on coral reefs?
The common name, Zooxanthellae, actually represents a group of single-celled algae that are symbiotic with corals and other reef organisms. These tiny photosynthetic organisms are present in the ocean as plankton before they enter the cells lining the “gut” of corals (gastrodermal cells). Once there they provide sugars, glycerol, and amino acids to the coral and in return the coral provides carbon dioxide, phosphates, and nitrogen compounds to the zooxanthellae.
Because the outer fleshy layers of a coral’s body (including tentacles) are actually transparent, the colorful layer of zooxanthellae in the gut cavity can be seen, essentially providing the coloration of the coral colony that we see when exploring a reef.