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Spatiotemporal variations of phytoplankton functional groups and environmental drivers over the past two decades in the Bohai, Yellow and East China Sea

  • Muhsan Ali Kalhoro (Marine College, Shandong University) ;
  • Veeranjaneyulu Chinta (Ningbo Institute of Digital Twin, Eastern Institute of Technology) ;
  • Muhammad Tahir (School of Space Science and Technology, Shandong University) ;
  • Yujie Sheng (Marine College, Shandong University) ;
  • Chunli Liu (Marine College, Shandong University) ;
  • Zhiyuan He (Marine College, Shandong University) ;
  • Zhenlin Liang (Marine College, Shandong University) ;
  • Jun Song (Operational Oceanography Institution, Dalian Ocean University) ;
  • Tony Song (Ningbo Institute of Digital Twin, Eastern Institute of Technology)
  • Received : 2025.09.20
  • Accepted : 2025.11.30
  • Published : 2025.12.15

Abstract

Phytoplankton, the primary producers of marine ecosystems, play a crucial role in sustaining primary production. This study investigates spatiotemporal variations in phytoplankton functional groups (PFGs) and their environmental drivers across the Bohai, Yellow, and East China Seas (BYECS) from 2003 to 2022. Sea surface temperature exhibited a significant warming trend (sea surface temperature [SST]; τ > 0.48, p < 0.01), increasing from 16.39℃ in 2011 to 17.98℃ in 2021, mean at 17.24 ± 0.39℃ and a breakpoint around 2009. Smaller phytoplankton, including prokaryotes (PROKAR, 27.86%; mean = 1.59 ± 0.96 mg m-3) and pico-phytoplankton (PICO, 28.99%; mean = 1.70 ± 0.95 mg m-3) showed strong negative correlations with SST (r = -0.64 and -0.69) and pronounced declines after 2015. Haptophytes and nanoplankton also decreased significantly (τ < -0.52, p < 0.001) with a breakpoint around 2011. In contrast, larger groups; diatoms (5.28%; mean = 0.41 ± 0.15 mg m-3) and micro-phytoplankton (MICRO, 8.44%; mean = 0.60 ± 0.19 mg m-3) were positively associated with SST (r = 0.38-0.49), indicating enhanced resilience under warming conditions. Total chlorophyll-a (TChl-a; 3.38 ± 3.74 mg m-3) declined significantly (τ < -0.57, p < 0.001) and showed a strong negative correlation with SST (r = -0.64), indicating reduced biomass after 2011. PICO and MICRO contributed 30-45% and 20-35% of TChl-a, respectively. Nutrients showed no significant long-term trends. Overall, findings reveal a warming-driven shift from small to larger phytoplankton groups, with decrease in TChl-a reflecting structural and productivity changes in the BYECS ecosystem. These findings are BYECS-specific and should be interpreted with caution due to uncertainties in remote-sensing PFG products and the potential influence of riverine inputs, stratification, and mixing.

Keywords

Acknowledgement

Present work is supported by the Shandong University, Marine College, Weihai (202367800206), and Ningbo Institute of Digital Twin present research is funded by corresponding author (Prof. Dr. Tony Song). Authors acknowledge the cooperation of Science and Technology Plan of Liaoning Province (2024JH2/102400061); Dalian Science and Technology Innovation Fund (2024JJ11PT007; Cai Yu); Dalian Science and Technology Program for Innovation Talents of Dalian (2022RJ06); Liaoning Province Education Department Scientific research platform construction project (LJ232410158056); Basic scientific research funds of Dalian Ocean University (2024JBPTZ001). We also acknowledge Dr. Cai Yu for his continues support throughout this study.

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