Abstract Krill are a key component of pelagic food webs where they are vital to the transfer of energy from phytoplankton to higher trophic levels. Krill have a high lipid content compared to other zooplankton and form dense aggregations, making them an important prey source for higher trophic level fish, seabirds, and marine mammals. The two dominant euphausiid species in the northern California Current (NCC) are Euphausia pacifica and Thysanoessa spinifera. E. pacifica is the most abundant species of euphausiid in the NCC, but T. spinifera has a higher potential energetic content due to its larger body size and higher lipid density. Most studies have inferred differences in lipid content and body condition between the two species, but few studies have quantified these differences in the NCC. Here, we report on the body condition, carbon and nitrogen content, as well as lipid and fatty acid composition of these two krill species, and the extent to which these metrics vary across season, year, and reproductive status. Body condition, elemental composition, and total lipids strongly differed between the species. T. spinifera had higher length-weight, Fulton’s K, hepato-somatic index, carbon to nitrogen ratio, total lipid per wet weight, and storage lipid compared to E. pacifica, indicating that T. spinifera has a higher energetic value for predators. However, there were strong seasonal differences in the energetics of T. spinifera. Carbon and lipids were highest in non-reproductive T. spinifera from August through October. Although there were strong ontogenetic and inter-specific differences, the lipid and fatty acid compositions of both species followed a seasonal progression characterized by low lipids during the pre-upwelling period, an increase in lipids, triacylglycerols, and diatom markers during upwelling, and increased proportions of dinoflagellate and bacterial diet markers during the fall post-upwelling period.

中文翻译：

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美国北加州洋流中太平洋磷虾和刺棘鱼的条件指标和脂质含量的比较

摘要 磷虾是远洋食物网的关键组成部分，它们对于将能量从浮游植物转移到更高的营养层至关重要。与其他浮游动物相比，磷虾具有较高的脂质含量并形成密集的聚集体，使它们成为较高营养级鱼类、海鸟和海洋哺乳动物的重要猎物来源。北加州洋流 (NCC) 中的两种主要磷虾种类是 Euphausia pacifica 和 Thysanoessa spinifera。E. pacifica 是 NCC 中最丰富的磷虾种类，但 T. spinifera 由于其更大的体型和更高的脂质密度而具有更高的潜在能量含量。大多数研究推断出这两个物种之间的脂质含量和身体状况存在差异，但很少有研究量化 NCC 中的这些差异。在这里，我们报告身体状况，碳和氮含量，以及这两种磷虾物种的脂质和脂肪酸组成，以及这些指标在不同季节、年份和繁殖状态之间变化的程度。不同物种之间的身体状况、元素组成和总脂质差异很大。与 E. pacifica 相比，T. spinifera 具有更高的身重、富尔顿 K、肝体指数、碳氮比、每湿重的总脂质和储存脂质，表明 T. spinifera 对捕食者具有更高的能量价值。然而，T. spinifera 的能量学存在强烈的季节性差异。从 8 月到 10 月，碳和脂类在非繁殖性刺棘果中最高。尽管存在强烈的个体遗传和种间差异，