Fatty acid composition of zooplankton, fishes and sea birds from the northern Humboldt Current System during Maria S. Merian cruise MSM80

Fatty acids were analyzed by gas chromatography using a DB-FFAP column of 30 m length and 0.25 mm inner diameter and a programmable temperature vaporizer injector. Following the trophic biomarker concept, the fatty acids 16:0, 20:5(n-3) and 22:6(n-3) were classified as typical components of biomembranes. High levels of 16:1(n−7) as well as 16:4(n−1) and 18:1(n−7) were used as diatom markers and 18:4(n−3) as fatty acid marker for dinoflagellates. The fatty acid 18:1(n-9) indicates carnivorous feeding. A carnivory index was applied based on the fatty acid ratio 18:1(n−9) / [16:1(n−7) + 16:4(n−1) + 18:1(n−7) + 18:4(n−3) + 18:1(n−9)] to reflect the proportion of carnivorous compared to herbivorous feeding in an organism. Fatty acid compositions of zooplankton and fish were taxon-specific and did not depend on sampling area or depth. Most species showed a dominance of typical membrane fatty acids, e.g., 16:0, 20:5(n-3) and 22:6(n-3). The dominant copepod Calanus chilensis had a low carnivory index and elevated amounts of diatom fatty acid markers which point to a predominantly herbivorous feeding. Among the krill species, Euphausia mucronata had the lowest carnivory index compared to the other euphausiids indicating a more herbivorous feeding. The squat lobster Pleuroncodes monodon had a significantly lower carnivory ratio compared to the deep-sea decapods Gennadas sp. and Acanthephyra sp. emphasizing its different trophic role compared to other decapods.本研究采用气相色谱法对脂肪酸进行分析，所用色谱柱为长度30 m、内径0.25 mm的DB-FFAP柱，并配备程序升温汽化进样器（programmable temperature vaporizer injector）。依据营养生物标志物（trophic biomarker）概念，将脂肪酸16:0、20:5(n-3)与22:6(n-3)归类为生物膜的典型组成成分。高含量的16:1(n−7)、16:4(n−1)及18:1(n−7)可作为硅藻标志物，而18:4(n−3)则为甲藻的脂肪酸标志物。脂肪酸18:1(n-9)可指示肉食性摄食行为。本研究基于脂肪酸比值18:1(n−9)/[16:1(n−7)+16:4(n−1)+18:1(n−7)+18:4(n−3)+18:1(n−9)]构建肉食性指数，用以反映生物体肉食性摄食相较于草食性摄食的占比。浮游动物与鱼类的脂肪酸组成具有类群特异性，且不受采样区域与采样深度的影响。多数物种的脂肪酸组成以典型膜脂肪酸为主，例如16:0、20:5(n-3)与22:6(n-3)。优势桡足类物种智利纺锤水蚤（Calanus chilensis）的肉食性指数较低，且硅藻脂肪酸标志物含量升高，提示其摄食策略以草食性为主。在磷虾类物种中，尖额磷虾（Euphausia mucronata）相较于其他磷虾目物种的肉食性指数最低，表明其摄食更偏向草食性。铠甲虾物种单齿扁虾（Pleuroncodes monodon）的肉食性比值显著低于深海十足类吉纳对虾属（Gennadas sp.）与刺螯虾属（Acanthephyra sp.），凸显出其与其他十足类物种不同的营养生态位。