Abstract Fatty acids (FA) have been used as diet biomarkers. They have proven to be a valuable method of defining food web relationships, trophic positioning, and the dietary behaviors of marine species. The endemic krill species of the Humboldt Current System (HCS), Euphausia mucronata, is the most abundant krill species over the continental shelf, usually associated with coastal upwelling zones. This study aimed to quantify the changes in the FA composition of E. mucronata in the coastal upwelling zone off Dichato in central Chile concerning the phytoplankton community and environmental variability. We hypothesized that E. mucronata changes its FA composition according to the functional species groups that structure the phytoplankton community as well as environmental variability. Krill, phytoplankton, and environmental datasets were analyzed using multivariate analyses, considering samplings from January 2013 to August 2014. The total concentration of FAs was 550.5 ng/g (n = 42) of which the 77% corresponded to six FAs: palmitoleic acid (16:1n7), palmitic acid (16:0), vaccenic acid (18:1), oleic acid (18:1n7), eicosapentaenoic acid (EPA, 20:5n3) and docosahexaenoic acid (DHA, 22:6n3). FA composition did not change according to neither the season nor sampling date. Seasonal changes were observed in both community structure of the phytoplankton (i.e. species composition and functional groups) and sea temperature. EPA/DHA ratio, PUFA/SFA ratio and carnivory variability were seasonally different suggesting that E. mucronata had mostly a diatom-based herbivorous habit during austral spring and summer and, it could have omnivore or carnivore habits during austral autumn and winter. Diatom and ciliate abundances and, sea temperature were the best predictor variables explaining 64% of the total variation in the FA composition. This study suggests that, despite seasonal environmental variation (biotic and abiotic), this krill species fed mainly diatoms and could shift its trophic habit to carnivory according to season of the year.

中文翻译：

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在智利中部 Dichato 海岸附近，与浮游植物群落和海洋变化有关的地方性洪堡海流磷虾中的脂肪酸组成，磷虾（甲壳纲，Euphausiacea）

摘要 脂肪酸 (FA) 已被用作饮食生物标志物。它们已被证明是定义食物网关系、营养定位和海洋物种饮食行为的一种有价值的方法。洪堡海流系统 (HCS) 的特有磷虾物种 Euphausia mucronata 是大陆架上最丰富的磷虾物种，通常与沿海上升流区有关。本研究旨在量化智利中部 Dichato 沿海上升流区 E. mucronata FA 组成的变化，涉及浮游植物群落和环境变异。我们假设 E. mucronata 根据构成浮游植物群落的功能物种群以及环境变异性来改变其 FA 组成。磷虾、浮游植物、考虑到 2013 年 1 月至 2014 年 8 月的采样，使用多变量分析对环境数据集进行了分析。 FA 的总浓度为 550.5 ng/g (n = 42)，其中 77% 对应于六种 FA：棕榈油酸 (16:1n7) 、棕榈酸 (16:0)、十油酸 (18:1)、油酸 (18:1n7)、二十碳五烯酸 (EPA, 20:5n3) 和二十二碳六烯酸 (DHA, 22:6n3)。FA 成分没有根据季节和采样日期而变化。在浮游植物群落结构（即物种组成和功能群）和海水温度中都观察到了季节性变化。EPA/DHA 比率、PUFA/SFA 比率和食肉变异性具有季节性差异，这表明 E. mucronata 在南方春季和夏季主要以硅藻为基础的食草习性，并且，它在南方秋冬季可能有杂食性或食肉性习性。硅藻和纤毛虫丰度以及海水温度是最好的预测变量，解释了 FA 组成总变化的 64%。这项研究表明，尽管存在季节性环境变化（生物和非生物），但这种磷虾物种主要以硅藻为食，并且可以根据一年中的季节将其营养习性转变为肉食性。