King Abdullah University of Science and Technology (KAUST), Red Sea Research Center, Biological and Environmental Science & Engineering Division, 23955-6900 Thuwal, Saudi Arabia.
King Abdullah University of Science and Technology (KAUST), Red Sea Research Center, Biological and Environmental Science & Engineering Division, 23955-6900 Thuwal, Saudi Arabia; Environment and Sustainability Institute, University of Exeter, TR10 9FE Penryn, United Kingdom.
Sci Total Environ. 2022 Jan 15;804:150098. doi: 10.1016/j.scitotenv.2021.150098. Epub 2021 Sep 4.
Contrary to epipelagic waters, where biogeochemical processes closely follow the light and dark periods, little is known about diel cycles in the ocean's mesopelagic realm. Here, we monitored the dynamics of dissolved organic matter (DOM) and planktonic heterotrophic prokaryotes every 2 h for one day at 0 and 550 m (a depth occupied by vertically migrating fishes during light hours) in oligotrophic waters of the central Red Sea. We additionally performed predator-free seawater incubations of samples collected from the same site both at midnight and at noon. Comparable in situ variability in microbial biomass and dissolved organic carbon concentration suggests a diel supply of fresh DOM in both layers. The presence of fishes in the mesopelagic zone during daytime likely promoted a sustained, longer growth of larger prokaryotic cells. The specific growth rates were consistently higher in the noon experiments from both depths (surface: 0.34 vs. 0.18 d, mesopelagic: 0.16 vs. 0.09 d). Heterotrophic prokaryotes in the mesopelagic layer were also more efficient at converting extant DOM into new biomass. These results suggest that the ocean's twilight zone receives a consistent diurnal supply of labile DOM from the diel vertical migration of fishes, enabling an unexpectedly active community of heterotrophic prokaryotes.
与表层水相反，生物地球化学过程紧密跟随光照和黑暗周期，而对海洋中层水的日周期循环知之甚少。在这里，我们在贫营养水域中，每 2 小时监测一次溶解有机物质 (DOM) 和浮游异养原核生物的动态，持续一天，深度分别为 0 米和 550 米（鱼类在白天垂直迁移时所处的深度）。我们还在同一地点进行了无捕食者的海水培养实验，采集时间分别为午夜和中午。微生物生物量和溶解有机碳浓度的相似原位可变性表明在这两层都有新鲜 DOM 的日供应。鱼类在中层水层中的日间存在可能促进了更大原核细胞的持续、更长时间的生长。来自两个深度（表层：0.34 比 0.18 天，中层：0.16 比 0.09 天）的中午实验的特定生长率始终较高。中层水层中的异养原核生物也更有效地将现存的 DOM 转化为新的生物量。这些结果表明，海洋的暮光区从鱼类的日垂直迁移中获得稳定的昼间易降解 DOM 供应，使异养原核生物群落变得异常活跃。
