C Y Wang, Wenbo Yang, Wenhua Bian, Guisheng Song, Yue Wang, Zhimeng Xu, X Wang, Longwen Fu, Junjian Wang, Zhilun Zhang, Yue Wang, Zhen Guo, Li Zhao
Pelagic microbial food webs (MFWs) functionally govern marine biogeochemical fluxes, oceanic productivity and climate feedbacks via complex trophic-level interactions, yet their compositional dynamics, trophic-level interactions and tightly coupled physicochemical driving factors remain insufficient in China's marginal seas (CMS: South China Sea, East China Sea, Yellow Sea, Bohai Sea). Here, we elucidate the MFW trophic structure (picoplankton [Pico], nanoplankton [Nano], microzooplankton [Micro]) and its physicochemical drivers across four CMS subzones during January 2025, utilizing flow cytometry, microscopy, and satellite remote sensing-derived hydrographic datasets. Results revealed a latitudinal northward shift in the MFW from Pico- to Micro-dominated assemblages. A size-structured framework was proposed, with consistent negative slopes for normalized abundance spectrum (-3.0 ± 0.2) and biomass spectrum (-1.8 ± 0.2)-validating metabolic ecological theory, with the biomass of 20-200 μm plankton accounting for 9.9% of that of 0.2-2.0 μm plankton. Specifically, trophic-level abundance ratios conformed to a ecological pyramid structure, with Pico: Micro and Nano: Micro ratios spanning 5 and 2 orders of magnitude, respectively. Concerning biotic-abiotic interplays, nutrient-driven bottom-up control emerged as the primary regulatory mechanism for both Pico and Nano spanning all seas except the Kuroshio-influenced zones. Multivariate analyses further identified synergistic environmental forcing-where nitrate-phosphate co-limitation interacts with strong current mixing-as the key modulator of MFW stability thresholds. Our findings provide a trait-based framework for predicting eutrophic marginal sea resilience and modeling carbon export under climate change.