Copepods are an important link in marine food webs, transferring crucial nutrients such as essential fatty acids (EFA) from primary producers to higher consumers. Yet data on lipid dynamics in marine ecosystems associated with small lipid-poor copepods are scarce. In this study, we used the coastal calanoid copepod Eurytemora herdmani, which is an opportunistic generalist feeder, to assess EFA-specific gross growth efficiency (GGEEFA), defined as the fraction of ingested EFA retained in copepod tissue. We conducted two eight-day feeding experiments with 13C-labeled phytoplankton to quantify incorporation and GGEEFA of eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA) in stage CV E. herdmani copepodites consuming either the EPA-replete diatom Thalassiosira weissflogii or the DHA-replete mixotrophic dinoflagellate Heterocapsa triquetra. EFA incorporation was quantified using gas chromatography. We recorded rapid shifts (within 48 h) in copepod tissue fatty acid (FA) composition following diet change, but not directly mirroring dietary algal FA. We also found high GGEEFA, with maxima of 46% and 61% for EPA and DHA, respectively, in copepods ingesting T. weissflogii and 39% and 87%, respectively, in copepods ingesting H. triquetra. GGEDHA remained higher than GGEEPA throughout the experiments regardless of dietary algae. GGEEFA decreased overall when copepods matured and produced nauplii, indicating EFA allocation for reproductive purposes. GGEDHA values in non-reproducing E. herdmani copepodites were high, suggesting that under predicted shifts in copepod community size structure, trophic transfer by small copepods could help compensate for DHA reductions resulting from lower abundances of large, lipid-rich species.

中文翻译：

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稳定同位素标记揭示了一种脂质贫乏的沿海类角足类动物必需脂肪酸生长效率的模式

桡足类是海洋食物网中的一个重要环节，将必需脂肪酸 (EFA) 等关键营养物质从初级生产者转移到高级消费者。然而，与小型贫脂桡足类相关的海洋生态系统中脂质动力学的数据很少。在这项研究中，我们使用沿海海角类桡足类 Eurytemora herdmani，这是一种机会主义的多面手饲养者，来评估 EFA 特定的总生长效率 (GGEEFA)，定义为保留在桡足类组织中的摄入 EFA 的分数。我们用 13C 标记的浮游植物进行了两个为期八天的饲养实验，以量化 CV E 阶段二十碳五烯酸（20:5n-3；EPA）和二十二碳六烯酸（22:6n-3；DHA）的掺入和 GGEEFA。herdmani 桡足类动物食用富含 EPA 的硅藻 Thalassiosira weissflogii 或富含 DHA 的混合营养型双鞭毛藻 Heterocapsa triquetra。使用气相色谱法对EFA掺入进行量化。我们记录了饮食改变后桡足类组织脂肪酸 (FA) 组成的快速变化（48 小时内），但没有直接反映饮食藻类 FA。我们还发现高 GGEEFA，EPA 和 DHA 的最大值分别在摄入 T. weissflogii 的桡足类中达到 46% 和 61%，在摄入 H. triquetra 的桡足类中分别达到 39% 和 87%。无论食用藻类如何，GGEDHA 在整个实验过程中始终高于 GGEEPA。当桡足类成熟并产生无节幼体时，GGEEFA 总体下降，表明 EFA 分配用于繁殖目的。非繁殖 E. herdmani 桡足类中的 GGEDHA 值很高，