Articles | Volume 10, issue 4
Biogeosciences, 10, 2775–2785, 2013

Special issue: Biogeochemistry and ecosystems in the western north Pacific...

Biogeosciences, 10, 2775–2785, 2013

Research article 29 Apr 2013

Research article | 29 Apr 2013

Seasonal and spatial comparisons of phytoplankton growth and mortality rates due to microzooplankton grazing in the northern South China Sea

B. Chen1, L. Zheng2, B. Huang1, S. Song3, and H. Liu2 B. Chen et al.
  • 1State Key Laboratory of Marine Environmental Science and Key Laboratory of the Ministry of Education for Coastal and Wetland Ecosystem, Xiamen University, Xiamen, Fujian, China
  • 2Division of Life Science, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
  • 3Key Laboratory of Marine Ecology and Environmental Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, Shandong, China

Abstract. We conducted a comprehensive investigation on the microzooplankton herbivory effect on phytoplankton in the northern South China Sea (SCS) using the seawater dilution technique at surface and deep chlorophyll maximum (DCM) layers on two cruises (July–August of 2009 and January of 2010). We compared vertical (surface vs. DCM), spatial (onshore vs. offshore), and seasonal (summer vs. winter) differences of phytoplankton growth (μ0) and microzooplankton grazing rates (m). During summer, both μ0 and m were significantly higher at the surface than at the DCM layer, which was below the mixed layer. During winter, surface μ0 was significantly higher than at the DCM, while m was not significantly different between the two layers, both of which were within the mixed layer. Surface μ0 was, on average, significantly higher in summer than in winter, while average surface m was not different between the two seasons. There were no cross-shelf gradients of μ0 in summer or winter surface waters. In surface waters, μ0 was not correlated with ambient nitrate concentrations, and the effect of nutrient enrichment on phytoplankton growth was not pronounced. There was a decreasing trend of m from shelf to basin surface waters in summer, but not in winter. Microzooplankton grazing effect on phytoplankton (m0) was relatively small in the summer basin waters, indicating a decoupling of microzooplankton grazing and phytoplankton growth at this time. On average, microzooplankton grazed 73% and 65% of the daily primary production in summer and winter, respectively.

Final-revised paper