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Zooxanthellae are a group of closely related dinoflagellates found in corals, anemones and some other cnidarians. It was once thought to be a single species, but now it is believed there multiple species and possibly even multiple genera of zooxanthellae. Organisms that contain zooxanthellae are called zooxanthellate and those without azooxanthellate.

Zooxanthellae live within the tissue of their hosts and provide the host with the products of photosynthesis: carbohydrates and oxygen. Carbohydrates only provide for the hosts energy needs and they still need other sources of nutrients. The host provides a "safe" place to live as well as the nutrients (nitrogen and phosphorus) that the zooxanthellae require.

Zooxanthellae are golden brown in colour and this is what gives corals and other cnidaria their basic colouration. Other coral colours (for example, blue, green, pink) come from pigments produce by the coral itself. The density of zooxanthellae in coral tissue ranges from 0.5 and 5 x l06 cell.cm-2 [1].



  1. Hoegh-Guldberg O. and Smith G.J. 1989. The effect of sudden changes in temperature, light and salinity on the population density and export of zooxanthellae from the reef corals Stylophora pistillata Esper and Seriatopora hystrix Dana. J. Exp. Mar. Biol. Ecol..129:279-303.