Ontogenetic influences on carbon flux in Aulactinia stelloides polyps (Anthozoa: Actiniaria) and their endosymbiotic algae

Abstract

Adult speciments of the tropical sea anemone Aulactinia stelloides Verrill (McMurrich, 1889) were collected from Andros Island, Bahamas, during October 1983, and the influence of animal developmental stage on the growth and photosynthetic capacity of endosymbiotic algae, as well as the utilization of translocated carbon by the animal, was investigated in adult and juvenile polyps using short-term 14C-bicarbonate labelling experiments. Zooxanthellae cell size was equivalent in adult (A) and juvenile (J) polyps. Light-saturated photosynthetic rates of zooxanthellae in juvenile polyps were double those in adult polyps (J: 5.7±0.2 μg C 106 cells-1 h-1 vs A: 2.4±0.8 μg C 106 cells-1 h-1), as were their cell-division frequencies (J: 4.4±0.5% vs A: 2.2±0.4%). Estimates of the percent of photosynthetically fixed 14C translocated to the anemone tissue by the zooxanthellae during 1 h incubations were lower for juvenile polyps (21%) than for adult polyps (29%). Zooxanthellae carbon-specific, translocation rates were, however, positively correlated with their specific photosynthetic rates. Partitioning of translocated carbon between the methanol-water-soluble, chloroform-soluble, and insoluble fractions of the host tissues exhibited significant variation with the developmental stage of the anemone. A significantly higher proportion of the fixed 14C activity in the animal tissues of adult polyps was recovered from the lipid (33%) compared to the particulate phase (18%). In juvenile polyps, the lipid and particulate fractions had equal proportions (25%) of the animal-tissue 14C activity. This study indicates that host developmental stage can influence zooxanthellae growth rates and consequently the rate of carbon flow within the association. The utilization of translocated carbon by the animal tissue is dependent on the biosynthetic requirements of its developmental stage in addition to its nutritional status.