Zooxanthellae: The yellow symbionts inside animals

Corals are associated with photosymbiotic unicellular algae and cyanobacteria. The unicellular algae are usually called zooxanthellae due to their yellow-brown color. The zooxanthellae are mainly classified as dinoflagellates to the genus Symbiodinium sp. The advantage of symbiosis is based on adaptations of transport and the exchange of nutritional resources, which allow it to be spread all over the tropical and some temperate oceans. Their existence over millions of years depends on the ability of the zooxanthellae, the host, and the holobiont as a whole unit to change, acclimate, and adapt in order to survive under developmental and stress.