SYMBIONT EXPULSION FROM THE ANEMONE ANTHOPLEURA ELEGANTISSIMA (BRANDT) (CNIDARIA; ANTHOZOA)

Abstract Expulsion, mitotic index (MI), and density of two species of symbiotic algae (zooxanthellae and zoochlorellae) in the sea anemone Anthopleura elegantissima (Brandt) were examined under three irradiance conditions. Expulsion of algae, regardless of species, increased directly with irradiance, while algal density remained independent of irradiance. The MI of algae in hospite was not significantly correlated with irradiance, although the MI of expelled algae was significantly higher than algae in hospite . The expulsion, MI, and density of algae in zoochlorellate anemones was consistently higher than in zooxanthellate anemones. The duration of cytokinesis ( t d ), not yet directly measured for the symbionts in A. Elegantissima , was estimated by comparing measured expulsion rates with algal growth needed to maintain constant densities within the host, yielding values of about 28 and 69 h for zooxanthellae and zoochlorellae, respectively.