Marine food webs are strongly size-structured and size-based analysis of communities is a useful approach to evaluate food webs in a way that can be compared across systems. Fatty acid analysis is commonly used to identify diet sources of species, offering a powerful complement to stable isotopes, but is rarely applied to size-structured communities. In this study, we used fatty acids and stable isotopes to characterize size-based variation in prey resources and trophic pathways over a nine-month temperate coastal ocean time series of seven plankton size classes, from > 0.7-μm particulate organic matter through > 2000-μm zooplankton. Zooplankton size classes were generally distinguishable by their dietary fatty acids, while stable isotopes revealed more seasonal variability. Fatty acids of zooplankton were correlated with those of their prey (particulate organic matter and smaller zooplankton) and identified trophic pathways, including widespread ties to the microbial food web. Diatom fatty acids also contributed to zooplankton but fall blooms were more important than spring. Concurrent isotope-based trophic position estimates and fatty acid markers of carnivory showed that some indicators (18:1ω9/18:1ω7) are not consistent across size classes, while others (DHA:EPA) are relatively reliable. Both analysis methods provided distinct information to build a more robust understanding of resource use. For example, fatty acid markers showed that trophic position was likely underestimated in 250-μm zooplankton, probably due to their consumption of protists with low isotopic fractionation factors. Applying fatty acid analysis to a size-structured framework provides more insight into trophic pathways than isotopes alone.

海洋食物网具有很强的规模结构，基于规模的群落分析是以可跨系统比较的方式评估食物网的有用方法。脂肪酸分析通常用于识别物种的饮食来源，为稳定同位素提供强大的补充，但很少应用于规模结构的群落。在这项研究中，我们使用脂肪酸和稳定同位素来表征七种浮游生物尺寸等级的九个月温带沿海海洋时间序列中猎物资源和营养途径的基于尺寸的变化，从> 0.7微米颗粒有机物到> 2000 -μm浮游动物。浮游动物的大小类别通常通过膳食脂肪酸来区分，而稳定同位素则显示出更多的季节性变化。浮游动物的脂肪酸与其猎物（颗粒有机物和较小的浮游动物）的脂肪酸相关，并确定了营养途径，包括与微生物食物网的广泛联系。硅藻脂肪酸也对浮游动物有贡献，但秋季水华比春季更重要。同时基于同位素的营养位置估计和食肉动物的脂肪酸标记表明，一些指标 (18:1ω9/18:1ω7) 在不同大小类别之间不一致，而其他指标 (DHA:EPA) 相对可靠。两种分析方法都提供了不同的信息，以更好地了解资源使用情况。例如，脂肪酸标记显示 250 μm 浮游动物的营养位置可能被低估，这可能是由于它们消耗同位素分馏因子较低的原生生物。将脂肪酸分析应用于尺寸结构框架可以比单独使用同位素更深入地了解营养途径。