The Biological Bulletin, Vol 184, Issue 2 223-229, Copyright © 1993 by Marine Biological Laboratory

PHYSIOLOGY

Photosynthesis and Retention of Zooxanthellae and Zoochlorellae Within the Aeolid Nudibranch Aeolidia papillosa

F. K. McFarland and G. Muller-Parker
Shannon Point Marine Center, Western Washington University, 1900 Shannon Point Road, Anacortes, Washington 98221

Both zooxanthellae and zoochlorellae are found in the cerata of Aeolidia papillosa after it has ingested symbiotic Anthopleura elegantissima containing these algae. High rates of photosynthesis were found in algae present in the cerata and in algae isolated from nudibranch feces. For algal cells present in the cerata of nudibranchs collected in June 1991, carbon fixation by zooxanthellae (1.18 +/- 0.36 pg C/cell/h) was significantly greater than carbon fixation by zoochlorellae (0.55 +/- 0.32 pg C/cell/h). Algal densities within the cerata of laboratory fed nudibranchs were significantly greater for zoochlorellae (175 +/- 82 cells/{mu}g protein, light treatment; 131 +/- 106 cells/{mu}g protein, dark treatment) than for zooxanthellae (38 +/- 18 cells/{mu}g protein, light; 53 +/- 30 cells/ {mu}g protein, dark). Ceratal densities of zooxanthellae (16 +/- 8 cells/{mu}g protein) in the field during January 1992 were low in comparison to ceratal densities in the laboratory--several of the nudibranchs in the field lacked any symbiotic algae, and zoochlorellae were always absent. Nudibranch algal densities were not stable and dropped rapidly if the nudibranchs were starved. Both zoochlorella and zooxanthella densities dropped to 0 cells/{mu}g protein within 11 days of starvation. While these results show that the relationship between A. papillosa and the two algae is not a stable symbiosis, the photosynthetic activity of the algae in the cerata suggests that the nudibranch and/or the algae may benefit from the association while it lasts.