Zooxanthellae

Zooxanthellae are are golden-brown intracellular endosymbionts (organisms that live within the body or cells of another) of various marine animals and protozoa, especially anthozoans such as the scleractinian (stony) corals and the tropical sea anemone, Aiptasia.

Reef-building corals are largely dependent on Zooxanthellae as they provide up to 90% of a coral’s energy requirements, in return the coral protects them and feeds them with nutrients as well as a constant supply of carbon dioxide for photosynthesis.