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Updated: Jun 9, 2026

Visualizing Oceanographic Data to Depict Long-term Changes in Phytoplankton
Published on: July 28, 2023
Picophytoplankton dominance driven by multi-factor eutrophication in a subtropical mariculture bay
Jin-Xiu Wang1, Fan-Zhou Kong2, Chao Liu3
1Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China.
None:
Under the influence of anthropogenic activities, phytoplankton communities in coastal oceans have undergone significant alterations. Qinzhou Bay (QB), a typical subtropical mariculture bay, has experienced rapid development of oyster mariculture industry and notable eutrophication, yet the systematic dynamics of phytoplankton communities and their driving mechanisms remain poorly characterized. In this study, monthly investigations were conducted from November 2021 to November 2022 to obtain physical, chemical, and phytoplankton data. The size structure, taxonomic composition, and spatiotemporal dynamics of phytoplankton assemblages were systematically analyzed using flow cytometry, pigment analysis, and high-throughput amplicon sequencing. Phytoplankton assemblages exhibited distinct spatial rather than temporal variability during the study period. The low-salinity eutrophic inner bay showed signs of phytoplankton miniaturization, with pico-sized prasinophytes and chlorophytes as characteristic taxa, whereas the nutrient-poor outer bay was dominated by relatively larger diatoms and dinoflagellates. Partial least squares regression (PLS-R) analysis identified phosphate (the most important), dissolved oxygen, temperature, salinity, and ammonium as the key environmental drivers shaping phytoplankton assemblages. Causal analysis based on partial least squares path modeling (PLS-PM) further demonstrated that nutrient status was the primary factor driving changes in phytoplankton size structure and taxonomic composition. Physical conditions and oyster aquaculture (via phosphate excretion) indirectly regulated phytoplankton assemblages mainly by modulating the nutrient regime in QB. Oyster grazing exerted a minor direct effect on phytoplankton size structure but substantially reduced phytoplankton biomass. Overall, the multi-factor eutrophication has promoted phytoplankton miniaturization in QB, raising concerns about potential food web imbalance and the risk of future pico-sized harmful algal blooms.
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