Photosynthesis and respiration of two species of algal symbionts in the Anemone Anthopleura elegantissima (Brandt) (Cnidaria; Anthozoa)

In parts of its range, the anemone Anthopleura elegantissima (Brandt) is populated by two different symbiotic algae: zoochlorellae and zooxanthellae. Anemones with exclusively one or the other symbiont were compared under identical conditions. A zooxanthella was about twice the volume and carbon content of a zoochlorella, and contained more chlorophyll. Zooxanthellae population density was 24% less than zoochlorellae, consequently zooxanthellae protein biomass per unit animal was only 58% greater than zoochlorellae. The mitotic index (MI) of zoochlorellae was almost 22 times greater than zooxanthellae, and the diel cell division pattern was asynchronous in both algae. Using duration of cytokinesis times (t(d)) of 28 and 69 h for zooxanthellae and zoochlorellae, respectively, we estimated that zoochlorellae grew eight times faster than zooxanthellae, with a commensurately shorter population doubling time. Zooxanthella respiration was two and a half times and net photosynthesis twice that of a zoochlorella; this coupled with a comparatively low growth rate allows the zooxanthellae population to potentially translocate almost five times as much carbon to its host as do zoochlorellae. The contribution of carbon to animal respiration (CZAR) was estimated at 48% for the zooxanthellate and only 9% for zoochlorellate anemones. It is suggested that these associations may be similar to ancestral symbioses.