Fatty acid profiles and stable isotope composition of Antarctic macroalgae: a baseline for a combined biomarker approach in food web studies

The Western Antarctic Peninsula supports a diverse assemblage of > 100 described macroalgal species that contribute to the base of coastal food webs, but their contribution to local nearshore food webs is still uncertain across larger spatial scales. The analysis of biomarkers, specifically fatty acids and stable isotopes, offers a tool to clarify the trophic role of Antarctic macroalgae. The aim of this study was to describe the fatty acid profiles and stable isotope values of 31 algal species from three divisions (Chlorophyta—1, Ochrophyta—8, Rhodophyta—22) collected at the same sites for both biomarkers. Of these, 13 species had no previously published fatty acid profiles. Most species were rich in polyunsaturated fatty acids (PUFAs), suggesting they are highly nutritious and could be a resource of essential fatty acids for consumers. This was specifically noticeable in the overall low PUFA ratio (∑ω6/∑ω3 ratio), with low ratios being an indicator of high nutritional quality for consumers. Fatty acid profiles of macroalgae grouped strongly by phylogeny (at the levels of division, order, and family), while stable isotope groupings were more driven by the physiological properties of the species. Specifically, some closely related red algal species exhibited very different stable isotope values based on their carbon concentrating mechanisms, with highly ¹³C-depleted values in several Rhodophyta species. The fact that the two biomarker approaches created different groupings of Antarctic macroalgae collected at the same locations emphasizes that their combined application can be a powerful tool in Antarctic coastal food web studies.