Weldrick Christine K, Trebilco Rowan, Swadling Kerrie M
Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tasmania, 7001, Australia.
Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Private Bag 80, Hobart, Tasmania, 7001, Australia.
Rapid Commun Mass Spectrom. 2019 Mar 30;33(6):569-578. doi: 10.1002/rcm.8384.
Stable isotope analysis (SIA) is a powerful tool to estimate dietary links between polar zooplankton. However, the presence of highly variable C-rich lipids may skew estimations as they are depleted in C relative to proteins and carbohydrates, consequently masking carbon signals from food sources. Lipid effects on pteropod-specific values requires examining, since accounting for lipids is rarely conducted among the few existing pteropod-related SIA studies. It is currently unclear whether lipid correction is necessary prior to SIA of pteropods.
Whole bodies of three species of pteropods (Clio pyramidata f. sulcata, Clione limacina antarctica, and Spongiobranchaea australis) sampled from the Southern Ocean were lipid-extracted chemically to test the effects on δ C and δ N values (n = 38 individuals in total). We determined the average change in δ C values for each treatment, and compared this offset with those from published normalization models. We tested lipid correction effects on isotopic niche dispersion metrics to compare interpretations surrounding food web dynamics.
Pteropods with lipids removed had δ C values up to 4.5‰ higher than bulk samples. However, lipid extraction also produced higher δ N values than bulk samples. Isotopic niche overlaps between untreated pteropods and their potential food sources were significantly different from overlaps generated between lipid-corrected pteropods and their potential food sources. Data converted using several published normalization models did not reveal significant differences among various calculated niche metrics, including standard ellipse and total area.
We recommend accounting for lipids via chemical extraction or mathematical normalization before applying SIA to calculate ecological niche metrics, particularly for organisms with moderate to high lipid content such as polar pteropods. Failure to account for lipids may result in misinterpretations of niche dimensions and overlap and, consequently, trophic interactions.
稳定同位素分析（SIA）是估计极地浮游动物之间饮食联系的有力工具。然而，富含碳的高变异性脂质的存在可能会使估计结果产生偏差，因为相对于蛋白质和碳水化合物，它们的碳含量较低，从而掩盖了来自食物来源的碳信号。由于在现有的少数与翼足类相关的SIA研究中很少考虑脂质因素，因此需要研究脂质对翼足类特定值的影响。目前尚不清楚在对翼足类进行SIA之前是否需要进行脂质校正。
从南大洋采集了三种翼足类动物（棱皮海若螺缢缩亚种、南极海天使和南方海绵鳃海若螺）的整体样本，通过化学方法进行脂质提取，以测试对δC和δN值的影响（总共n = 38个个体）。我们确定了每种处理的δC值的平均变化，并将此偏移量与已发表的归一化模型的偏移量进行比较。我们测试了脂质校正对同位素生态位分散指标的影响，以比较围绕食物网动态的解释。
去除脂质的翼足类动物的δC值比整体样本高出4.5‰。然而，脂质提取也产生了比整体样本更高的δN值。未处理的翼足类动物与其潜在食物来源之间的同位素生态位重叠与脂质校正后的翼足类动物与其潜在食物来源之间产生的重叠显著不同。使用几种已发表的归一化模型转换的数据在各种计算的生态位指标（包括标准椭圆和总面积）之间没有显示出显著差异。
我们建议在应用SIA计算生态位指标之前，通过化学提取或数学归一化来考虑脂质因素，特别是对于脂质含量中等至高的生物，如极地翼足类动物。不考虑脂质因素可能会导致对生态位维度和重叠的误解，进而导致对营养相互作用的误解。
