Oxygen as a limiting factor in phototaxis and in intraclonal spacing of the sea anemone Anthopleura elegantissima

Phototaxis in Anthopleura elegantissima, a sea anemone symbiotic with zooxanthellae, was investigated with special reference to oxygen as a possible controlling factor. Under high oxygen concentrations in seawater, movement towards light was not observed for symbiotic anamones as it was under normal oxygen concentrations. Both aposymbiotic and symbiotic anemones demonstrated movement towards high oxygen concentrations in seawater. Oxygen is, therefore, implicated as a controlling factor in phototaxis. Under laboratory conditions, increased intraclonal spacing occurred with low oxygen concentrations in seawater. In the field, individuals in symbiotic clones were spaced significantly closer than in aposymbiotic clones. Since intraclonal spacing is controlled by oxygen in the laboratory, spacing may also be affected in the field by oxygen; symbiotic clones may be spaced closer because they have better oxygen availability than do aposymbiotic clones.