|Abstract: ||abstract:Weather conditions in our study area during the northeasterly (NE) monsoon season are usually rough, and it is difficult to sample on board a boat in winter; therefore, knowledge of copepod assemblages is very limited. This study was carried out at the beginning and end of the NE monsoon in Dec. 2003 and Feb. 2004, respectively, in an attempt to understand variations in copepod compositions. The Kuroshio water (KW) with high temperatures and salinities flowed past our eastern stations and affected the hydrographic conditions in these 2 study periods. At the same time, the low-temperature and -salinity China coastal water (CCW) flowed southward into our western stations in the early winter, while the Kuroshio branch water (KBW) was also introduced in our study area, and affected the hydrographic
conditions of station D-2 in late winter. The average chlorophyll-a concentration was higher (37.0 mg/m2) in the late and lower (14.8 mg/m2
) in the early northeasterly monsoon. In the present study, 109 species of copepods belonging to 5 orders, 26 families, and 48 genera were identified. Copepod species diversity and evenness increased in the CCW but decreased in the KW from early to late winter, and were higher in the KW than in the CCW in our 2 study periods. Indicator species of the CCW in early winter were Paracalanus aculeatus (72.5%) and Euchaeta concinna (72.0%), which changed to Corycaeus (Ditrichocorycaeus) affinis (96.7%), Calanus
sinicus (95.9%), P. parvus (94.6), and Acrocalanus gracilis (90.9%) in late winter; those of the KW in early winter were Pleuromamma gracilis (100%), Calanopia minor (94.4%), Rhincalanus nasutus (92.3%), Temoropia mayumbaensis (90.7%), Calocalanus pavo (80.1%), Clausocalanus lividus (77.7%), Lucicutia flavicornis (73.4%), Acartia danae (72.6%), which were replaced by Aetideus acutus (100%), Copilia mirabilis (100%),
Farranula concinna (96.5%) and Calanoides carinatus (75.3%) in late winter.