Planktivorous vendace (Coregonus albula) utilise algae-derived fatty acids for biomass increase and lipid deposition

Spatial and seasonal variation in the abundance and composition of phytoplankton and other basal resources (bacteria, terrestrial detritus) influence the availability of essen-tial polyunsaturated fatty acids (PUFA) for upper trophic levels in lake food webs. We studied accumulation, composition and content of fatty acids in planktivorous ven-dace (Coregonus albula) muscle tissue during the summer feeding period (May to late September) in six boreal lakes. Vendace muscle fatty acid content increased from ~17.7 mg/g DW to ~28.1 mg/g DW from spring to summer, corresponding to a ~59% increase in total fatty acids. PUFA accounted for 45%–65% of all fatty acids, and the most abundant fatty acid was docosahexaenoic acid (DHA, 22:6n- 3). The DHA con-tent remained relatively constant throughout the sampling period (~7–8 mg/g DW), but the proportion of DHA decreased from ~40% in spring to ~30% in summer and autumn. The decrease in DHA proportion was due to accumulation of other fatty acids, primarily C18 PUFA (predominantly synthetised by algae) and monounsaturated fatty acids. A similar fatty acid accumulation pattern was observed in lipid storing co-pepods, an important prey for planktivorous vendace. The abundance of bacterial and terrestrial biomarker fatty acids in vendace muscle and prey items was low (<5% and <0.1% respectively). The increase in weight and the deposition of internal energy stores in vendace were achieved predominantly by algae- based food chain. This has ecological implications, as vendace requires sufficient lipid stores for reproduction in autumn and survival over winter.