Abstract
Abstract. This study evaluates spatial variations in zooplankton community structure and potential controlling factors along the Japanese coast under the influence of the coastal branch of the Tsushima Warm Current (CBTWC). Variations in the density of morphologically identified zooplankton in the surface layer in May were investigated for a 15-year period. The density of zooplankton (individuals per cubic meter) varied between sampling stations, but there was no consistent west–east trend. Instead, there were different zooplankton community structures in the west and east, with that in Toyama Bay particularly distinct: Corycaeus affinis and Calanus sinicus were dominant in the west and Oithona atlantica was dominant in Toyama Bay. Distance-based redundancy analysis (db-RDA) was used to characterize the variation in zooplankton community structure, and four axes (RD1–4) provided significant explanation. RD2–4 only explained < 4.8 % of variation in the zooplankton community and did not show significant spatial difference; however, RD1, which explained 89.9 % of variation, did vary spatially. Positive and negative species scores on RD1 represent warm- and cold-water species, respectively, and their variation was mainly explained by water column mean temperature, and it is considered to vary spatially with the CBTWC. The CBTWC intrusion to the cold Toyama Bay is weak and occasional due to the submarine canyon structure of the bay. Therefore, the varying bathymetric characteristics along the Japanese coast of the Japan Sea generate the spatial variation in zooplankton community structure, and dominance of warm-water species can be considered an indicator of the CBTWC.
Highlights
IntroductionPlankton community structure varies in accordance with currents (Russell, 1935), and changes in ocean currents cause fisheries’ regimes to shift, such as from sardine to anchovy and back (Chavez et al, 2003)
Ocean currents transport water with heat and solved materials, and they are related to climate properties and distributions of dissolved and particulate matter (Thorpe, 2010).The biological importance of ocean currents has been accepted for a century, since Hjort (1914), and is especially applicable in coastal areas which only cover 7 % of the ocean but support 90 % of global fish catches (Pauly et al, 2002).Plankton community structure varies in accordance with currents (Russell, 1935), and changes in ocean currents cause fisheries’ regimes to shift, such as from sardine to anchovy and back (Chavez et al, 2003)
Ocean currents are important for zooplankton abundance and community structure: the Gulf Stream affects the abundance of copepods, Calanus finmarchicus and C. helgolandicus, in the European coastal seas (Frid and Huliselan, 1996; Reid et al, 2003), and the copepod species richness varies with the inflow of source water in the California current (Hooff and Peterson, 2006)
Summary
Plankton community structure varies in accordance with currents (Russell, 1935), and changes in ocean currents cause fisheries’ regimes to shift, such as from sardine to anchovy and back (Chavez et al, 2003). Ocean currents are important for zooplankton abundance and community structure: the Gulf Stream affects the abundance of copepods, Calanus finmarchicus and C. helgolandicus, in the European coastal seas (Frid and Huliselan, 1996; Reid et al, 2003), and the copepod species richness varies with the inflow of source water in the California current (Hooff and Peterson, 2006). Ocean currents and water temperature, nutrient supply, and many other factors affect zooplankton abundance and community structure; monitoring results of zooplankton abundance and community usually reflect hydrometeorological change (Beaugrand, 2005).
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