Preprints
https://doi.org/10.5194/bg-2021-226
https://doi.org/10.5194/bg-2021-226

  01 Sep 2021

01 Sep 2021

Review status: this preprint is currently under review for the journal BG.

Biophysical controls on seasonal changes in the structure, growth, and grazing of the size-fractioned phytoplankton community in the northern South China Sea 

Yuan Dong1,2, Qian Li1,2,3, Zhengchao Wu1,2, Yiping Shuai1,3, Zijia Liu1,3, Zaiming Ge1,3, Weiwen Zhou1,3, and Yinchao Chen1,3 Yuan Dong et al.
  • 1State key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China
  • 2Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, China
  • 3College of Marine Science, University of the Chinese Academy of Sciences, Beijing, China

Abstract. The size-fractionated phytoplankton growth and microzooplankton grazing are crucial for the temporal change of community size-structure, regulating not only trophic transfer but also carbon cycle of the ocean. However, the size-dependent growth and grazing dynamics on monthly or an annual basis are less addressed in the coastal ocean. In this paper, the seasonal responses of the size-fractionated phytoplankton growth and grazing to environmental change were examined over a one-year period at a coastal site of the northern South China Sea. We found a nanophytoplankton dominated community with strong seasonal variations of all size classes. Phytoplankton community growth rate was positively correlated to nutrients with community grazing rate correlating to the total chlorophyll-a at the station, reflecting a combined bottom-up and top-down effect on phytoplankton population dynamics. Further analyses suggested that the specific growth rate of microphytoplankton was significantly influenced by phosphate with that of nanophytoplankton by light, although picophytoplankton growth was controlled by both nitrate and temperature. In addition, the specific grazing rate of nanophytoplankton was well correlated to phytoplankton standing stock, while those of micro- and pico-compartments were negatively influenced by ciliate abundance and salinity. Finally, a lower grazing impact for micro-cells (38 %) than nano- and pico-cells (72 % and 60 %, respectively) may support a size-selective grazing of microzooplankton on small cells at this eutrophic system.

Yuan Dong et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-226', Anonymous Referee #1, 07 Sep 2021
  • RC2: 'Comment on bg-2021-226', Anonymous Referee #2, 02 Oct 2021
  • RC3: 'Comment on bg-2021-226', Anonymous Referee #3, 11 Oct 2021

Yuan Dong et al.

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Short summary
Temporal change of plankton growth & grazing are less known in the coastal ocean, not to mention the relevant controlling mechanisms. Here, we performed monthly size-specific dilution experiments outside a eutrophic estuary over a year cycle. Phytoplankton growth was correlated to nutrients with grazing mortality to total chlorophyll-a. A selective grazing on small cells may be important for maintaining high abundance of large chain-forming diatoms in this eutrophic system.
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