Trophic links between the epipelagic (< 200 m) and mesopelagic layers of the Indian Ocean were investigated by carbon and nitrogen stable isotope ratios of 2405 samples collected from 2002 to 2016, and that encompass the base of trophic webs, and primary, secondary and tertiary consumers. The samples include particulate organic matter, gastropods, gelatinous organisms such as salps and pyrosomes, crustaceans, mesopelagic fishes, micronektonic and nektonic squids, tuna and swordfish. Stable δC and δN values were used to investigate trophic and resource partitioning between epipelagic mesopelagic (migrators and non-migrators), feeding patterns (zooplanktivorous micronektivorous), and at seamounts and off-seamount locations. We also investigated how contrasting environmental conditions within two biogeochemical provinces, the ISSG (Indian South Subtropical Gyre) and EAFR (East African Coastal Province), influenced stable isotope patterns. Our data suggest that broad-scale biogeochemical differences and local environmental conditions significantly shape trophic and resource partitioning. In oligotrophic systems, epipelagic migrating and non epipelagic-migrating organisms rely on food webs where suspended particles are N-enriched and organic matter recycled/re-processed. We show that seamounts form strong isotopic topographic barriers (which we define as “isobiome”) that impact the trophic linkages/connections between epipelagic migrants and non-epipelagic migrants, and those with zooplanktivorous feeding patterns. This study reveals that the trophic and resource partitioning in the ocean is more complex than initially thought, when environmental variability, bathymetric gradients, and a wider range of samples are taken into account compared to earlier studies. We also showed that a warmer ocean led to a reduction in productivity, lower values of δC and δN, and potential shifts in food web trophic structure that remain to be investigated further. Finally, we discuss how important it is to unravel this complexity on a global scale given the vulnerability of epipelagic and mesopelagic communities due to anthropogenic pressures in the Anthropocene.

中文翻译：

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环境变异性影响海洋省份上层和中层生物群落之间的营养和资源分配：对全球海洋变化的影响


通过 2002 年至 2016 年收集的 2405 个样本的碳和氮稳定同位素比，研究了印度洋表层 (< 200 m) 和中表层之间的营养联系，这些样本涵盖了营养网的基础以及初级、次级和三级消费者。样品包括颗粒有机物、腹足动物、胶质生物（如樽海鞘和火体）、甲壳类动物、中层鱼类、微游动和游动鱿鱼、金枪鱼和旗鱼。稳定的 δ13C 和 δ15N 值用于研究上层中层生物（洄游生物和非洄游生物）、摄食模式（食浮游动物、微食动物）以及海山和海山外位置之间的营养和资源分配。我们还研究了 ISSG（印度南亚热带环流）和 EAFR（东非沿海省）这两个生物地球化学省内的对比环境条件如何影响稳定同位素模式。我们的数据表明，大范围的生物地球化学差异和当地环境条件显着影响营养和资源分配。在寡营养系统中，上层洄游和非上层洄游生物依赖于食物网，其中悬浮颗粒富含氮并且有机物被回收/再加工。我们表明，海山形成了强大的同位素地形屏障（我们将其定义为“同生物群”），影响了表层移民和非表层移民之间的营养联系/联系，以及那些具有浮游动物摄食模式的移民。这项研究表明，与早期研究相比，当考虑到环境变化、测深梯度和更广泛的样本时，海洋中的营养和资源分配比最初想象的更加复杂。 我们还表明，海洋变暖导致生产力下降、δ13C 和 δ1N 值降低以及食物网营养结构的潜在变化，这些变化仍有待进一步研究。最后，我们讨论了在全球范围内解开这种复杂性的重要性，因为人类世的人为压力导致了上层和中层群落的脆弱性。