This study quantified natural seasonal variability in heterotrophic and autotrophic input to the energy budget of the temperate symbiotic anemone, Anemonia viridis, to determine the consequential effects on growth and reproductive capacity of the species. Most physiological investigations involving symbiotic Cnidaria are based on static time periods. With growing concerns of climate change and global warming, it is increasingly topical to assess such issues as a function of environmental variability. Temperate symbioses, naturally exposed to pronounced seasonal fluctuations, are ideal systems for investigating temporal variability in energetic terms. Heterotrophic and autotrophic input of a standard specimen of A. viridis accounted for 52.5 and 47.5 % of the annual energy
budget respectively, with daily scope for growth being substantially greater during spring and summer (111- 201 J) compared to autumn and winter (29-43 J). Autotrophic input was proportionately greater in winter and autumn (77-81 % ) compared to spring and summer (33-42 %), and due to reduced respiratory costs, a greater contribution of zooxanthellae to host animal respiration was revealed in winter (193 %), compared to all other seasons (85-136 %). Furthermore, A. viridis were incapable of surviving through heterotrophy alone, dispelling the hypothesis that symbionts are parasitic during reduced photosynthetic input. 22.7 % of annual input was attributed to metabolism, with growth including asexual fission and sexual reproduction accounting for 1.9 and 3.7 % respectively, with 71.7 % attributed to secretion. The budget was never in deficit indicating a constant capacity for production, despite marked seasonal variability. The efficiency of A. viridis may lie in their ability to adopt different energetic strategies, employing an exploitative strategy during spring and summer and a conservative strategy during winter. Such inherent plasticity may augment their physiological niche,
enabling greater habitat exploitation, and perhaps more importantly, adaptation in the face of environmental change.