Gelatinous zooplankton are increasingly recognized as key components of pelagic ecosystems, and there have been many recent insights into their ecology and roles in food webs. To examine the trophic ecology of siphonophores (Cnidaria, Hydrozoa), we used bulk (carbon and nitrogen) and compound‐specific (nitrogen) isotope analysis of individual amino acids (CSIA‐AA). We collected samples of 15 siphonophore genera using blue‐water diving, midwater trawls, and remotely operated vehicles in the California Current Ecosystem, from 0 to 3000 m. We examined the basal resources supporting siphonophore nutrition by comparing their isotope values to those of contemporaneously collected sinking and suspended particles (0–500 m). Stable isotope values provided novel insights into siphonophore trophic ecology, indicating considerable niche overlap between calycophoran and physonect siphonophores. However, there were clear relationships between siphonophore trophic positions and phylogeny, and the highest siphonophore trophic positions were restricted to physonects. Bulk and source amino acid nitrogen isotope (δ15N) values of siphonophores and suspended particles all increased significantly with increasing collection depth. In contrast, siphonophore trophic positions did not increase with increasing collection depth. This suggests that microbially reworked, deep, suspended particles with higher δ15N values than surface particles, likely indirectly support deep‐pelagic siphonophores. Siphonophores feed upon a range of prey, from small crustaceans to fishes, and we show that their measured trophic positions reflect this trophic diversity, spanning 1.5 trophic levels (range 2.4–4.0). Further, we demonstrate that CSIA‐AA can elucidate the feeding ecology of gelatinous zooplankton and distinguish between nutritional resources across vertical habitats. These findings improve our understanding of the functional roles of gelatinous zooplankton and energy flow through pelagic food webs.

中文翻译：

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远洋食物网中凝胶状捕食者的垂直营养结构和生态位划分：来自管水母稳定同位素的见解

胶状浮游动物越来越被认为是远洋生态系统的关键组成部分，最近对其生态学和在食物网中的作用有了许多见解。为了研究管水母动物（刺胞动物、水螅动物）的营养生态学，我们使用了单个氨基酸的本体（碳和氮）和化合物特异性（氮）同位素分析（CSIA-AA）。我们利用深海潜水、中层拖网和遥控车辆在加州海流生态系统中从 0 米到 3000 米的深度采集了 15 个管水母属的样本。我们通过将其同位素值与同时收集的下沉和悬浮颗粒（0-500 m）的同位素值进行比较，检查了支持管水母营养的基础资源。稳定同位素值为管水母营养生态学提供了新的见解，表明管水母和管水母之间存在相当大的生态位重叠。然而，管水母的营养位置与系统发育之间存在明显的关系，并且管水母的最高营养位置仅限于physonects。本体和源氨基酸氮同位素 (δ15N)管水母和悬浮颗粒的值均随着收集深度的增加而显着增加。相反，管水母的营养位置并没有随着收集深度的增加而增加。这表明微生物改造的深层悬浮颗粒具有更高的 δ15N 值高于表面颗粒，可能间接支持深海管水母。管水母以各种猎物为食，从小型甲壳类动物到鱼类，我们发现它们测量的营养位置反映了这种营养多样性，跨越 1.5 个营养级别（范围 2.4-4.0）。此外，我们证明 CSIA-AA 可以阐明胶状浮游动物的摄食生态，并区分垂直栖息地的营养资源。这些发现提高了我们对凝胶状浮游动物的功能作用和通过远洋食物网的能量流的理解。