Seasonal variability in plankton food web structure and trophodynamics in the neritic area of Sagami Bay,Japan |
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| Authors: | Koichi Ara Juro Hiromi |
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| Institution: | (1) Department of Marine Science and Resources, College of Bioresource Sciences, Nihon University, Fujisawa Kanagawa, 252-0880, Japan;(2) Research Division in Biological Environment Studies, Graduate School of Bioresource Sciences, Nihon University, Fujisawa Kanagawa, 252-0880, Japan;(3) Department of Bioenvironmental and Agricultural Engineering, College of Bioresource Sciences, Nihon University, Fujisawa Kanagawa, 252-0880, Japan;(4) National Research Institute of Fisheries Science, Fisheries Research Agency, Kanazawa-ku, Yokohama Kanagawa, 236-8648, Japan;(5) Present address: Department of Aquatic Bioscience, Faculty of Bioindustry, Tokyo University of Agriculture, Abashiri Hokkaido, 099-2493, Japan |
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| Abstract: | The plankton food web structure and trophodynamics in the neritic area of Sagami Bay were investigated from January 2003 to
December 2005, based on abundance, biomass, production rate and nutritional requirements of pico- (0.2–2 μm), nano- (2–20
μm), micro- (20–200 μm) and mesoplankton (>200 μm: mainly copepods CI-CVI) at 0–10 m depth. The average carbon biomass of
the total plankton community was higher in spring and summer (1.452 and 1.466 g C m−2, respectively) than in winter and autumn (0.676 and 0.686 g C m−2, respectively). The average values of primary production and of production rate and food requirement of heterotrophic organisms
were higher in summer than in other seasons. During the study period the biomass, production rate and food requirement of
small heterotrophs (i.e. bacteria: BA; heterotrophic nanoflagellates: HNF; microzooplankton: MZ) were much higher than those
of copepod secondary (CSP) and tertiary producers (CTP), indicating that the microbial food web was the main route of carbon
flow from phytoplankton (PP) to CSP and CTP, rather than the grazing food chain. In particular, during summer and autumn the
biomass of pico- and nano-size PP plus BA was greater than that of micro-size PP, suggesting the high prevalence of the microbial
food web (pico-/nanophytoplankton/BA-HNF/MZ-copepods). During winter and spring, the biomass of micro-size PP was greater
than that of pico- and nano-size PP plus BA, suggesting that the indirect route (microphytoplankton-MZ-copepods) probably
prevailed, while the microbial food web might be important. |
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