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.
Wang et al. (Tue,) studied this question.