Influence of lipid separation on the trophic interpretation of fatty acids

Abstract

Fatty acids (FAs) are a common tool to investigate trophic ecology due to the transfer of several FAs across trophic levels. However, some dietary FAs are modified to maintain homeostasis. Therefore, for trophic purposes, there is the question of whether to separate lipid fractions into fatty acids that are physiologically regulated (structural, polar lipids) and those which are not (reserve, neutral lipids). This study compared the effect of lipid separation prior to FA analysis (total lipid versus neutral lipid fraction) on the ecological interpretations for several pelagic and benthic marine consumers. A tissue with high total lipid content, the hepatopancreas (total lipid content >17% dry weight), had similar FA proportions (in relative abundance) in both total and neutral lipid fractions. For lean muscle (total lipid content <10% dry weight), differences in FA proportions between lipid fractions were species-specific. Proportions of some FAs can be converted from one fraction to the other using simple linear models (e.g., 22:6n-3 and 18:1n-9 for pelagic consumers) but most differences in FA proportions cannot be corrected which should be considered when comparing data from the literature. The present study should be extended to other species and tissues to further elucidate the importance of tissue total lipid content and neutral to total lipid ratio on the difference of dietary interpretations between total and neutral FA proportions. In particular, it would be useful for marine trophodynamic studies to define a guideline of the tissue total lipid content above which lipid separation is not required.