Arctic pelagic amphipods: lipid dynamics and life strategy

Polar regions are characterized by a strong seasonality in primary production and distinct fluctuations in food supply. The storage of energy in the form of lipids is expected to follow a seasonal pattern; however, year-round observations are lacking. The seasonal variations of lipid classes and fatty acid compositions of four pelagic amphipods have been investigated. Individuals were collected at various depths during summer and winter expeditions to the Fram Strait and Svalbard archipelago (788–818N). Our results show a year-round dominance of wax esters and triacylglycerols over phospholipids for Themisto abyssorum, Themisto libellula, Themisto compressa and Cyclocaris guilelmi. High levels of the Calanus-marker fatty acids 20:1 and 22:1 (both isomers) during summer and winter indicated that all four species are part of the Calanus-based food web. Specific fatty acid trophic markers for diatoms and flagellates indicated that the lipid-based energy transfer could be traced back to the respective algal sources.We found a distinct difference between animals collected from very deep and shallow waters, which indicates that the lipid reservoir of these amphipods and their biochemical modifications seem to buffer seasonal variations in available prey and to allow an active, predatory life-style year-round in Arctic waters