Grazing by microzooplankton and copepods on the microbial food web in spring in the southern Yellow Sea, China
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RESEARCH PAPER
Grazing by microzooplankton and copepods on the microbial food web in spring in the southern Yellow Sea, China Yuan Zhao1,2,7 · Yi Dong1,2,7 · Haibo Li1,2,7 · Shiquan Lin3 · Lingfeng Huang4,5 · Tian Xiao1,2,7 · Gerald Gregori6 · Li Zhao1,2,7 · Wuchang Zhang1,2,7 Received: 6 March 2020 / Accepted: 6 May 2020 © The Author(s) 2020
Abstract Assessment of microzooplankton and copepods grazing pressure on picoplankton is a key requirement for resolving the microbial food web efficiency. Although microzooplankton grazing on picoplankton has been extensively studied, the impact of microzooplankton on different groups of picoplankton, i.e., heterotrophic bacteria, Synechococcus and picoeukaryotes have rarely been compared. Furthermore, in the very few existing studies there is no consistent evidence of an enhancing or restraining effect of copepods on picoplankton. More studies are needed to improve our understanding of the influence of microzooplankton and copepod on picoplankton. Dilution incubations and copepod addition incubations were performed during a cruise to the southern Yellow Sea on May 16–29, 2007. The bulk grazing of microzooplankton and the calanoid copepod Calanus sinicus on phytoplankton, flagellates and picoplankton was estimated. Stations were divided into either eutrophic or oligotrophic according to the nutrient and biological parameters. Picoplankton comprised a large part of the diet of microzooplankton in the central oligotrophic area, while phytoplankton was the main food of microzooplankton in the coastal eutrophic area. In the central oligotrophic area, microzooplankton preferred grazing on Synechococcus. After copepod addition, ciliate abundance decreased while Synechococcus abundance increased (382%, 64% and 64% at three experimental stations, respectively), indicating strong grazing pressure of microzooplankton on Synechococcus. Our results suggest that Synechococcus might be an essential carbon source the planktonic food web in the oligotrophic waters of southern Yellow Sea. Keywords Microzooplankton · Dilution incubations · Copepod addition incubations · Ciliate · Picoplankton · Yellow Sea
Introduction The planktonic microbial food web is composed of microzooplankton, phytoplankton, including flagellates, microphytoplankton, cyanobacteria and picoeukaryotes, heterotrophic prokaryotes (bacteria and archaea, hereafter referred to “bacteria”) and virioplankton (Azam et al. 1983; Ducklow 1983). There are complex trophic relationships between these microorganisms (Sherr and Sherr 2008). Planktonic ciliates are often the dominant Edited by Chengchao Chen. * Li Zhao [email protected] * Wuchang Zhang [email protected] Extended author information available on the last page of the article
microzooplankton (Pierce and Turner 1992) and are well recognized as a key component of many plankton food web models (Baretta et al. 1995; Kishi et al. 2007). Microzooplankton can affect picoplankton either directly by grazing or indirectly by feeding on other picoplankton grazers, such as h
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