Tracking dietary fatty acids in triacylglycerols and phospholipids of zooplankton

Abstract

Abstract Fatty acids (FA) in lake zooplankton are largely provided by dietary FA and affected by taxonomic composition of zooplankton, temperature, and other environmental conditions. However, the extent to which dietary FA are retained and/or bioconverted in zooplankton remains unclear. In this lake study, we examined how dietary FA (seston), temperature and physico‐chemical variables (i.e., concentrations of chlorophyll a, dissolved organic carbon, nitrate, ammonium, phosphate) explained the FA variation in membrane (phospholipids; PL) and storage (triacylglycerols; TAG) lipids of zooplankton. We tested the hypotheses that: (1) increasing dietary FA increases the FA content stored as TAG by zooplankton, whereas the FA content in PL remains unaffected by naturally occurring changes in dietary FA supply; and (2) FA in seston better predict the FA variations stored by zooplankton as TAG, whereas lake temperature better predicts the FA variations in zooplankton PL. Results show that an increase in dietary polyunsaturated FA increased polyunsaturated FA in TAG and PL of zooplankton, but not eicosapentaenoic acid or docosahexaenoic acid in PL. Moreover, the FA content of seston was more similar to that of zooplankton TAG than it was to the content of PL, indicating major taxon‐specific differences in membrane FA. Dietary FA are a major predictor of FA in TAG of zooplankton, while the taxonomic composition of zooplankton is a major predictor of FA in PL. Temperature and physico‐chemical variables explained little of the variations in zooplankton FA. This field study improves our understanding of how FA in PL and TAG of different zooplankton taxa respond to changes of dietary FA, temperature, concentrations of chlorophyll‐a, dissolved organic carbon, nitrate, ammonium, and phosphate to fulfil their physiological requirements.