Beschreibung:
<p>In a field study, we analyzed the fatty acid (FA) composition of the benthic generalist <italic>Asellus aquaticus</italic> collected from boreal lakes, ponds, and streams across gradients in ambient nutrient levels. In laboratory feeding experiments, we tested the diet-quality and seasonal effects on somatic growth and FAs of spring- and autumn-collected <italic>Asellus</italic> that were fed four different diets containing increasing concentrations of polyunsaturated FAs (PUFA): conditioned leaf litter, algal flakes, mixed litter and algal flakes (Mixed), or Mixed plus fish-food flakes. Ambient nutrients were strong determinants of FA variation of field <italic>Asellus</italic>, explaining > 44% in total. The ratios of eicosapentaenoic acid (EPA) to total FAs, EPA : ω3, and ω3 : ω6 of <italic>Asellus</italic> increased up to four times with increasing trophic state and decreasing humic matter content, likely because dietary ω3 FAs were more prevalent in benthic habitats of eutrophic than of oligotrophic systems. In the feeding trials, growth of <italic>Asellus</italic> collected in both seasons was markedly lower on leaf litter than on higher PUFA diets. However, autumn-collected <italic>Asellus</italic> fed a Mixed or Mixed+fish-food diet grew 3–10 times faster, but retained < 50% EPA and PUFA than spring counterparts. <italic>Asellus</italic> optimized PUFA accumulation in spring but somatic growth in autumn. Our field survey suggests ambient nutrient concentrations modify dietary PUFA supply from basal resources, while laboratory studies show that growth response and PUFA accumulation of <italic>Asellus</italic> differ between seasons, likely due to its season-specific physiological status and diet quality. An increase in nutrients will release benthic consumers from growth limitation and favor more efficient trophic transfer.</p>