Spatial variations in zooplankton community structure along the Japanese coastline in the Japan Sea: influence of the coastal current

Abstract

Abstract. This study evaluates spatial variations in zooplankton community structure and potential controlling factors along 10 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 15 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 <6.5% of variation in the zooplankton community and did not show significant spatial difference; however, RD1, which explained 84.6% 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. Water column mean temperature is highly correlated 20 with mean and maximum salinity, and it is considered to vary spatially with the CBTWC. The CBTWC intrusion to 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.

Interannual variations in diet of Japanese jack mackerel (Trachurus japonicus) juveniles in the southwestern Sea of Japan in relation to recent growth rate

“…One possibility would be the following explanation. In our study area, the TWC largely influences both the hydrographic condition and zooplankton distribution (Hirakawa et al, 1995; Katoh, 1994; Kodama et al, 2018; Ogawa, 1983). The intensity of the TWC in 2013 was estimated to be stronger compared to the other 2 years, based on observations and analysis by the Japan Meteorological Agency (https://www.data.jma.go.jp/gmd/kaiyou/data/db/kaikyo/tsushima/tsushima_area.html) (Data S2).…”