Sea anemones are known to have symbiotic algae living within their gastrodermal cells. An example of a sea anemone containing both species is Anthopleura xanthogrammica . The proportion of each symbiont is dependent upon the water temperature. At intermediate temperatures, the numbers of each species are close to equal. The zoochlorellae excrete only small amounts of fixed carbon, so when the zoochlorellae predominate, the algae must supply something else to make up for it.
Sea anemones position themselves in a way as to increase light exposure to their symbionts.
When their tentacles are relaxed, the algae lie in a single layer. When the anemone contracts its tentacles, the gastrodermal cells shrink and the algae lie on top of each other. The zooxanthellae benefit by receiving carbon dioxide from the respiration of the host, nutrients such as nitrogen and phosphorus from the hosts metabolism which are then recycled back and forth between the host and the symbiont, and a shelter in which to live. The sea anemone benefits by receiving oxygen and food in the form of glycerol, glucose and alanine from photosynthesis. As the polyp dies, their shells do not decay and new polyps grow over them.