Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN, United States of America.
Illinois-Indiana College Sea Grant Program, West Lafayette, IN, United States of America.
PLoS One. 2024 Jul 22;19(7):e0304089. doi: 10.1371/journal.pone.0304089. eCollection 2024.
Aquatic food webs are spatially complex, potentially contributing to intraspecific variability in production pathway reliance of intermediate trophic level consumers. Variation in trophic reliance may be described by well-established trophic indicators, like stable isotope ratios (δ13C, δ15N), along with emerging trophic indicators, such as fatty acid composition. We evaluated stable isotope ratios and fatty acid profiles of European smelt (Osmerus eperlanus) among and within distinct regions of three large Swedish lakes (Hjälmaren, Mälaren, Vättern) which differed in trophic status. We expected that smelts in more oligotrophic lakes and regions would be characterized by distinct stable isotope signatures and fatty acid profiles, with particularly high polyunsaturated fatty acid (PUFA) relative levels. However, we acknowledge that frequent movement of smelts among regions may serve to spatially integrate their diet and lead to limited within-lake variation in stable isotope ratios and fatty acid composition. As expected, in comparison with more productive lakes (i.e., Hjälmaren and Mälaren), smelts from ultra-oligotrophic Vättern were characterized by low δ15N, high δ13C and high percent of a dominant PUFA, docosahexaenoic acid (DHA). Smelts from different regions of the morphometrically complex Mälaren displayed differential stable isotope ratios and fatty acid relative concentrations, which were consistent with within-lake differences in productivity and water residence times, suggesting that smelts in this lake forage locally within distinct regions. Finally, at the individual smelt level there were particularly strong and consistent associations between a well-established trophic indicator (δ13C) and percent DHA, suggesting that the relative concentration of this fatty acid may be a useful additional trophic indicator for smelt.
水生食物网具有空间复杂性，可能会导致中间营养级消费者对生产途径的依赖存在种内变异性。营养依赖的变化可以通过成熟的营养指标来描述，如稳定同位素比值（δ13C、δ15N），以及新兴的营养指标，如脂肪酸组成。我们评估了三种瑞典大湖（Hjälmaren、Mälaren、Vättern）不同营养状态下的欧洲胡瓜鱼（Osmerus eperlanus）的稳定同位素比值和脂肪酸谱。我们预计，在贫营养湖泊和地区的胡瓜鱼将具有独特的稳定同位素特征和脂肪酸谱，特别是具有较高的多不饱和脂肪酸（PUFA）相对水平。然而，我们承认，胡瓜鱼在各地区之间频繁的移动可能会使其饮食在空间上得到整合，并导致湖泊内稳定同位素比值和脂肪酸组成的变化有限。正如预期的那样，与生产力更高的湖泊（即 Hjälmaren 和 Mälaren）相比，来自超贫营养的 Vättern 的胡瓜鱼的 δ15N 较低、δ13C 较高、占主导地位的多不饱和脂肪酸（DHA）的百分比较高。来自形态复杂的 Mälaren 不同地区的胡瓜鱼表现出不同的稳定同位素比值和脂肪酸相对浓度，这与湖泊内生产力和水停留时间的差异一致，表明该湖的胡瓜鱼在不同的区域内进行局部觅食。最后，在个体胡瓜鱼水平上，一个成熟的营养指标（δ13C）和 DHA 的百分比之间存在特别强而一致的关联，这表明这种脂肪酸的相对浓度可能是胡瓜鱼的一个有用的额外营养指标。
