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.
Interdecadal change in the upper water column environment and spring diatom community structure in the Japan Sea: an early summer hypothesis