Translocation of Photosynthetic Carbon From Two Algal Symbionts to the Sea Anemone Anthopleura elegantissima.

Abstract

The intertidal sea anemone Anthopleura elegantissima contains two symbiotic algae, zoochlorellae and zooxanthellae, in the Northern Puget Sound region. Possible nutritional advantages to hosting one algal symbiont over the other were explored by comparing the photosynthetic and carbon translocation rates of both symbionts under different environmental conditions. Each alga translocated 30% of photosynthetically fixed carbon in freshly collected anemones, although zoochlorellae fixed and translocated less carbon than zooxanthellae. The total amount of carbon translocated to the host was equivalent because densities of zoochlorellae were two to three times greater than were densities of zooxanthellae. In A. elegantissima maintained under high and low irradiance (100 and 10 {mu}mol photons/m2/s) at 20{deg}C and 13{deg}C for 21 days, both algae fixed and translocated carbon at greater rates at 20{deg}C (translocation rates: 0.38 pg C /zoochlorella/h; 1.12 pg C /zooxanthella/h) than at 13{deg}C (translocation rates: 0.06 pg C /zoochlorella/h; 0.37 pg C /zooxanthella/h). However, zoochlorellate anemones received 3.5 times less carbon at 20{deg}C than at 13{deg}C because the higher temperature caused a significant reduction in the density of zoochlorellae. Environmental variables, like temperature, that influence the densities of the two symbionts will affect their relative nutritional contribution to the host. Whether these differences in carbon translocation rates of the two algal symbionts affect the ecology of their anemone host awaits further investigation.