The ecology of vertically migrating mesopelagic micronekton is affected by physical properties of their environment. Increased light attenuation in particle-rich productive waters, as well as low oxygen conditions decrease the migration amplitude. This likely has implications on the trophic organisation of micronekton communities, which are predominantly governed by niche partitioning in the vertical dimension. We investigated trophic structures of pelagic communities in the eastern tropical North Atlantic by comparing micronekton species assemblages from the low-oxygen region influenced by Mauritanian upwelling between 8° and 11° N (LO) and the less productive and more oxygenated equatorial area between 0 and 4°N (EQ). We analysed stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in body tissues of 35 species of mesopelagic fishes, four species of cephalopods, two species of cnidarians, and two species of decapods and used these values as a proxy for their trophic niche and correlated them with the traits feeding guild, migration pattern, mean depth of occurrence and body size. Our results demonstrate significant regional differences in the food web structure and vertical trophic interactions of the investigated micronekton assemblages. Diurnally migrating fishes that predominantly feed on copepods exhibited higher δ¹⁵N values in the LO (9.6‰) than in the EQ (8.9‰), reflecting changes in baseline values of pelagic tunicates. Contrary, all other Feeding – Migrator guilds show lower or similar δ¹⁵N values in the LO compared to the EQ, indicating reduced isotopic enrichment between trophic levels (TL) in the LO compared to the EQ. Further, a generally lower δ¹⁵N enrichment between TL3 – TL4 compared to TL2 – TL3 was observed (LO: TL2 – TL3: ~2.2‰, TL3 – TL4: ~1.2‰; EQ: TL2 – TL3: ~3.5‰, TL3 – TL4: ~2.2‰). Quantitative isotopic niche metrics suggest enhanced competition in trophic niche space, whereas relative isotopic niche positions indicate an increased importance of food from lower trophic levels (non-crustacean and/or gelatinous prey resources) for fishes from the LO compared to the EQ. The absence of a depth-related increase in δ¹⁵N values of partial- and nonmigrators of the LO is contrary to results from the EQ and previously published data. Low δ¹⁵N values in partially and nonmigrating micronektonivores of the LO in comparison with those of the EQ could be due to feeding on lower trophic prey components in the LO, as is indicated by an overlap in isotopic niche with that of partially and nonmigrating mixed crustacean feeders in the LO. Alternatively, driving mechanisms could be the consumption of prey from shallower waters, regional differences in δ¹⁵N enrichment, species-specific ecological differences or a combination of these processes. Each of these explanations is likely tightly correlated to a vertical biogeochemical structuring effect of low oxygen midwater layers fuelled by high nitrate inputs from the Mauritanian upwelling region. Our study provides crucial ecological insights for a better understanding of large-scale gradients in micronekton migration patterns.

垂直迁移的中弹性微神经的生态受到其环境物理特性的影响。在富含颗粒物的生产水中增加的光衰减以及低氧条件降低了迁移幅度。这可能对微尼克群落的营养组织有影响，微群落主要由垂直方向的生态位分配控制。我们通过比较受毛里塔尼亚上涌8°至11°N（LO）和低产且含氧量较大的赤道区域在0和0之间的影响的低氧区的微尼克物种组合，研究了北热带东部大西洋中上层群落的营养结构。 4°N（EQ）。我们分析了碳（δ的稳定同位素¹³ C）和氮（δ ¹⁵N）在35种中生鱼类，4种头足类动物，2种刺胞类动物和2种十足类动物的身体组织中，并将这些值用作其营养位的代表，并将其与摄食公会，迁徙方式，平均发生深度和身体大小。我们的结果表明，在食物网结构和所研究的微分子组合的垂直营养相互作用方面存在明显的区域差异。上桡足类主要饲料昼夜迁移鱼表现出较高的δ ¹⁵比在EQ（8.9‰）在LO（9.6‰）的N个值，反映了浮游被囊动物的基线值的变化。相反，所有其他料-迁移行会显示出较低的或相似δ ¹⁵LO中的N值与EQ相比，表明LO中的营养级（TL）与EQ相比同位素富集减少。此外，通常降低δ ¹⁵ TL3之间的N个富集- TL4相比TL2 -观察（LO TL3：TL2 - TL3：〜2.2‰，TL3 - TL4：〜1.2‰; EQ：TL2 - TL3：〜3.5‰，TL3 – TL4：〜2.2‰）。定量同位素生态位指标表明，营养生态位空间竞争加剧，而相对同位素生态位位置表明，与EQ相比，来自LO的鱼类的营养水平较低（非甲壳类和/或胶状猎物资源）对食物的重要性增加。不存在在一个δ深度相关增加^15个partial-的N个值并nonmigrators LO的是违背从EQ结果和此前公布的数据。低Δ ¹⁵与均衡器相比，LO的部分和非迁徙微肾小动物的N值可能是由于以LO中较低的营养猎物为食，这表明同位素利基与部分和不迁徙的混合甲壳类动物的食盐重叠。 LO。另外，驱动机构可能是猎物从较浅的水域，区域差异的消费δ ¹⁵N富集，特定物种的生态差异或这些过程的组合。这些解释中的每一个都可能与毛里塔尼亚上升区的高硝酸盐输入推动的低氧中间水层的垂直生物地球化学结构化作用紧密相关。我们的研究提供了至关重要的生态学见识，以更好地了解微浮游生物迁移模式中的大规模梯度。