Carbon isotope composition of fatty acids and sterols in the scleractinian coral Turbinaria reniformis: Effect of light and feeding
Treignier, C., I. Tolosa, R. Grover, S. Reynaud, and C. Ferrier-Pagès
Limnol. Oceanogr., 54(6), 2009, 1933–1940

The effect of auto- and heterotrophy on the carbon isotope composition (d¹³C) of fatty acids (FA) and sterols was studied in the scleractinian coral Turbinaria reniformis. Colonies were maintained in aquaria for 6 weeks under two light levels (100 and 300 mmol photons m^-2 s^-1) and/or two trophic conditions (starved and fed twice a week with zooplankton). In high-light conditions, lipid biomarkers, both in the zooxanthellae and animal tissue, presented significantly higher d¹³C values compared to those exposed to low light, supporting the widespread theory of enhanced ¹³C fixation with increasing irradiance and photosynthesis. This result and the similar lipid d¹³C-values of the host and the symbionts are a strong indication that most lipids are synthesized by the zooxanthellae. Feeding had a smaller effect than light on the lipid d¹³C-signatures and a more pronounced effect at low-light level. Despite the depleted d¹³C values of the zooplankton lipids, slight enrichment in ¹³C was observed in some FA from the host and zooxanthellae, whereas the main host sterol was depleted in ¹³C. These differences between FA and sterols give evidence for different biosynthesis pathways: FA might have been synthesized from the assimilation of carbohydrates or amino acids contained in the food, whereas sterols might derive from modification of dietary lipids.