The Significance of the Relationship between Actinians and Zooxanthellae

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Abstract
1. Actinia equina and Anemonia sulcata are two anemones which respectively lack and possess symbiotic algae. If kept for several months in complete darkness Actinia retains its colour and Anemonia becomes white through loss of its algae. 2. Such alga-free Anemonia will continue to live in a healthy condition if supplied with solid food and sufficient dissolved oxygen. 3. In darkness the oxygen consumption of Actinia is lower than that of either normal or alga-free Anemonia about half that of the latter. 4. In daylight the photosynthetic activity of the algae is more than sufficient to meet the needs of normal Anemonia, so that oxygen is added to the water. 5. The phosphate excretion of Actinia is about half as much as that alga-free Anemonia and the phosphate excretion of neither is appreciable affected by change from darkness to light. 6. In daylight the phosphate excretion of normal Anemonia is less than that of alga-free Anemonia. There is a great reduction of phosphate excretion by normal Anemonia in darkness. 7. Apparently the alga benefits from the association by using the anemone as a source of phosphorus, the extent of phosphate utilization being diminished during photosynthesis. 8. Presumably the Anemonia benefit by insurance against oxygen starvation when isolated in small pools of stagnant water during daylight.

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