Understanding seasonal trophic linkages via fatty acid profiles, and bulk, lipid and fatty acid-specific stable isotopes in Arctic marine invertebrates
Climate change is having profound impacts on Arctic ecosystems with important implications for coastal productivity and food web dynamics. The goal of this research was to determine seasonal variations in diets of 15 key invertebrate taxa in lagoon ecosystems along the Alaska Beaufort Sea coast. We used a combination of fatty acid biomarkers and stable carbon isotope measurements of whole animals, total lipid extracts, and individual fatty acids to identify the relative importance of terrestrial organic matter and in-situ primary production to their diets.
Invertebrates collected during full-ice cover (April), ice break-up (June) and open water (August) displayed shifts in seasonal contributions of terrestrial and marine food sources. Invertebrates collected in April had higher proportions of terrestrial fatty acid markers (e.g. 18:2n-6), consistent with depletions in both bulk and 18:2n-6 δ13C values in the same month. In June and August, invertebrates were characterized by greater contributions from in-situ algal sources and higher proportions of essential fatty acids (e.g. DHA and EPA). Proportions of bacterial fatty acids in invertebrates reveal patterns of differential feeding modes across taxa. In addition, while whole body and fatty acid-specific stable isotopes differed across seasons, total lipid δ13C did not change significantly. These results highlight the current role of various carbon sources to Arctic coastal food webs, which may change with future warming. Fatty acid biomarkers and stable isotopes are powerful tools for food web studies and in elucidating the complex pathways by which a variety of carbon sources are assimilated by estuarine fauna.