Krill Sterol and Lipid Class Fatty Acid Data

Fatty acid analysis is a powerful tool in food web research for estimating dietary sources in marine predators. However, the utility of fatty acids as dietary indicators from whole lipid samples, rather than from separate lipid classes, has been questioned. Samples are often collected at a single time point, precluding seasonal dietary comparisons. We investigated variations in the fatty acid composition of structural (phospholipids) and storage lipids (triacylglycerols) of Antarctic krill (Euphausia superba) using fisheries samples obtained over one year. Seasonal variation was observed in fatty acid biomarkers within triacylglycerol and phospholipid fractions of krill. Fatty acids in krill triacylglycerols (thought to better represent recent diet), reflected omnivorous feeding with highest percentages of flagellate biomarkers (18:4n-3) in summer, and diatom biomarkers (16:1n-7c) in autumn, winter and spring. Carnivory biomarkers (∑ 20:1 + 22:1 and 18:1n-9c/18:1n-7c) in krill were greater in autumn. Phospholipid fatty acids were less variable and higher in 20:5n-3 and 22:6n-3, which are essential components of cell membranes. Sterol composition did not yield detailed dietary information, but percentages of the major krill sterol, cholesterol, were significantly higher in winter and spring compared with summer and autumn. Unexpectedly, 18:4n-3 and copepod markers ∑ 20:1 + 22:1 were not strongly associated with the triacylglycerol fraction during some seasons. Krill may mobilise 18:4n-3 to phospholipids for conversion to long chain polyunsaturated fatty acids, which would have implications for its role as a dietary biomarker. For the first time, we demonstrate the dynamic seasonal relationship between specific biomarkers and krill lipid classes.

脂肪酸分析（Fatty acid analysis）是食物网（Food web）研究中用于估算海洋捕食者膳食来源的重要技术手段。然而，学界对以完整脂质样本而非分离脂质类别为来源的脂肪酸膳食指示物的实用性尚存质疑。现有研究多仅单次采集样本，无法开展季节性膳食对比分析。本研究依托为期一年的渔业捕捞样本，探究了南极磷虾（Euphausia superba）结构脂质（磷脂（Phospholipids））与储存脂质（三酰甘油（Triacylglycerols））的脂肪酸组成变化。研究发现，磷虾三酰甘油与磷脂组分中的脂肪酸生物标志物（Fatty acid biomarker）存在显著季节性变化。磷虾三酰甘油中的脂肪酸（被认为更能反映近期膳食摄入情况）体现出杂食性摄食特征：夏季时鞭毛虫生物标志物（18:4n-3）占比最高，而秋、冬、春三季硅藻生物标志物（16:1n-7c）占比最高。磷虾体内的食肉性生物标志物（∑20:1 + 22:1及18:1n-9c/18:1n-7c）在秋季占比更高。磷脂源性脂肪酸的波动幅度更小，且20:5n-3与22:6n-3的占比更高，二者均为细胞膜的必需组成成分。甾醇（Sterol）组成无法提供详细的膳食信息，但磷虾主要甾醇胆固醇（Cholesterol）的占比在冬、春两季显著高于夏、秋两季。令人意外的是，在部分季节中，18:4n-3与桡足类生物标志物∑20:1 + 22:1与三酰甘油组分并未呈现显著关联。磷虾可能会将18:4n-3转运至磷脂中，用于合成长链多不饱和脂肪酸（Long-chain polyunsaturated fatty acids），这一过程将影响其作为膳食生物标志物的应用价值。本研究首次揭示了特定生物标志物与磷虾脂质类别之间的动态季节性关联。