The Barents Sea is a hotspot for environmental change due to global warming. These changes impact the structure and functioning of the marine ecosystem year-round, and it is therefore important to gain knowledge on trophic relationships and the energy flow from primary producers, i.e., ice algae (sympagic algae) and phytoplankton (pelagic algae) to consumers over the entire seasonal cycle. By using different lipid components as trophic markers, we provide seasonal coverage of the carbon and food-source composition of five of the most abundant and ecologically important zooplankton taxa inhabiting the Barents Sea: copepods, krill, amphipods, pteropods and chaetognaths. Based on the composition of algal-produced fatty acid (FA) markers, carbon-source composition of the zooplankton species reflected changes in the production and availability of food resources during different periods of the year. For example, relative proportions of the dinoflagellate/Phaeocystis FA marker 18:4(n-3) peaked during summer in Calanus copepods, the amphipod Themisto abyssorum and the chaetognath Pseudosagitta maxima, when the production of this FA reached maximum concentrations in phytoplankton. The composition of carnivory FAs (relative contribution of copepod-associated FAs, ratio 18:1(n-9)/18:1(n-7)) and the ratio of zoo- to phytosterols indicated that most grazers relied more on heterotrophic prey during polar night and spring while switching to a more algae-based diet during the summer. Based on source-specific highly branched isoprenoids (HBIs), sympagic carbon had generally a minor contribution to the nutrition of the zooplankton community, particularly during winter and spring when sympagic HBIs were virtually undetected in the animals. In contrast, sympagic HBI metabolites were detected in krill, amphipods and the pteropod Clione limacina during summer and autumn. The krill Meganyctiphanes norvegica was unique in terms of its HBI composition as the only species containing both sympagic and pelagic HBIs during spring. Our results indicate that the Barents Sea zooplankton community is largely based on pelagic carbon, while sympagic carbon is only supplementing species-specific diets, mostly during the second half of the year. This relatively low trophic dependency on sea-ice algae might be an indication of the resilience of this food web towards ongoing sea-ice decline that causes changes to the timing and availability of sympagic and pelagic carbon and food sources.

中文翻译：

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冰藻是巴伦支海浮游动物群落的补充食物，而不是主要能源


由于全球变暖，巴伦支海是环境变化的热点地区。这些变化全年影响着海洋生态系统的结构和功能，因此，了解营养关系和从初级生产者（即冰藻（共生藻类）和浮游植物（中上层藻类）到消费者的能量流在整个季节周期中非常重要。通过使用不同的脂质成分作为营养标志物，我们提供了栖息在巴伦支海的五个最丰富和生态最重要的浮游动物分类群的碳和食物来源组成的季节性覆盖：桡足类、磷虾、片足类、翼足类和毛皮颌类。根据藻类产生的脂肪酸 （FA） 标志物的组成，浮游动物物种的碳源组成反映了一年中不同时期食物资源的生产和可用性的变化。例如，甲藻/Phaeocystis FA 标志物 18：4（n-3） 的相对比例在夏季在桡足类、角足类 Themisto abyssorum 和 chaetognath Pseudosagitta maxima 中达到峰值，此时这种 FA 的产生在浮游植物中达到最大浓度。食肉动物 FA 的组成（桡足类相关 FA 的相对贡献，比率 18：1（n-9）/18：1（n-7）））和动物园与植物甾醇的比例表明，大多数食草动物在极夜和春季更多地依赖异养猎物，而在夏季转向更多以藻类为基础的饮食。基于源特异性高度支化的异戊二烯类 （HBI），共性碳通常对浮游动物群落的营养贡献很小，尤其是在冬季和春季，此时共性 HBI 在动物中几乎未检测到。 相比之下，夏季和秋季在磷虾、片足类和翼足类 Clione limacina 中检测到共性 HBI 代谢物。南虾 Meganyctiphanes norvegica 在其 HBI 组成方面是独一无二的，是唯一在春季同时包含共栖和中上层 HBI 的物种。我们的结果表明，巴伦支海浮游动物群落主要基于中上层碳，而共生碳仅在下半年补充特定物种的饮食。这种对海冰藻类的营养级依赖相对较低可能表明该食物网对持续的海冰减少具有复原力，海冰减少导致共生和中上层碳和食物来源的时间和可用性发生变化。