Permalink : http://hdl.handle.net/2115/54866

KEYWORDS : Mesozooplankton;Community;Species diversity;Copepods;Nauplii;Appendicularians;Molluscs;Tsushima warm current

Seasonal changes in the zooplankton community in Ishikari Bay, northern Japan Sea were studied based on monthly samples collected by vertical hauls of a 100 μm mesh NORPAC net from March 2001 to May 2002. Zooplankton abundance peaked in May and was mainly composed of copepodid stages of copepods. Cluster analysis of copepod abundance separated the community into two main groups : group A was observed from January to June (winter and spring) and group B from July to December (summer and autumn). Groups A and B were composed of cold and warm water species, respectively. Species diversity was high for group B. As the second dominant taxa, copepod nauplii dominated during winter and spring, whereas molluscs and appendicularians were abundant during summer and autumn. Copepod nauplii in winter and spring likely reflect the copepod reproduction initiated by spring the phytoplankton bloom. Molluscs in summer and autumn were composed of planktonic larvae of benthos (=meroplankton). Appendicularians during summer and autumn are oceanic and considered to have been transported by the Tsushima warm current. High copepod species diversity during summer and autumn might also be related to the Tsushima warm current.