Algal Symbiosis in Bunodeopsis: Sea Anemones with "Auxiliary" Structures

This study describes the photobiology of two tropical species of the symbiotic sea anemone genus Bunodeopsis from Discovery Bay, Jamaica, B. antilliensis was found in shallow water (0.3m) and experienced higher irradiance levels than B. globulifera from deeper water (3 m). Both species contained symbiotic dinoflagellates of the genus Symbiodinium within the endodermal cells. The external morphology and expansion-contraction behavior of the two anemone species were closely linked to symbiont distribution. B. antilliensis had large vesicles (2.6 mm3), with 88.5% of the symbiont population in the lower column and basal disk and 11.5% in the tentacles and upper column, and was contracted under normal daylight illumination. In contrast, B. globulifera had small vesicles (0.2 mm3), with 55.5% of the symbionts in the lower column and basal disk and 44.5% in the tentacles and upper column, and was expanded under illumination. The photosynthetic physiology of the symbionts indicated that those from B. globulifera were adapted to lower host habitat irradiances than were those from B. antilliensis. The symbionts from B. globulifera had a significantly higher chlorophyll a content (7.34 +/- 0.77 pg·cell-1) and photosynthetic efficiency (0.24 μgO2·106 cells.h-1/μmol photons·m-2·s-1) and lower saturation irradiance (277 +/- 18 μmol photons·m-2·s-1) than those from B. antilliensis, 4.51 +/- 0.29 pg.cell-1, 0.17 μgO2.106 cells· h-1/μmol photons·m-2·s-1 and 436 +/- 78 μmol photons·m-2·s-1, respectively. The calculated rate of carbon translocation in both species of Bunodeopsis (97%) was high and reflected the low algal protein biomass ratios (2%) and population growth rates (<0.1·day-1). The CZAR values in B. antilliensis (109%) and B. globulifera (92%) suggest that both species are potentially autotrophic with respect to carbon available for animal respiration.