A 5-year study of the influence of the northeast and southwest monsoons on copepod assemblages in the boundary coastal waters between the East China Sea and the Taiwan Strait

Danshuei River in the northwestern tip of Taiwan dischargesinto the boundary coastal waters between the East China Seaand the Taiwan Strait. We conducted a 5-year study between October1998 and September 2003 to assess the influence of the northeast(NE) and the southwest (SW) monsoons on copepod assemblagesin the area. A total of 110 copepod species were identified.Temora turbinata, Paracalanus aculeatus, Acrocalanus gibber,Parvocalanus crassirostris and Oithona rigida comprised 80%of the copepod assemblages that consisted of coastal speciesfrom the East China Sea and species associated with the KuroshioBranch Current. The effect of the NE monsoon was observed duringa short period of each winter when species such as Calanus sinicuswere transported into the study area by the China Coastal Current.In summer, species such as A. gibber, Acrocalanus gracilis andCanthocalanus pauper may be transported into the study areafrom Southern Taiwan by the combined effect of the SW monsoonand the Kuroshio Current. Influence of the NE monsoon on thecopepod assemblages in terms of introduction of species fromthe Yellow Sea and the East China Sea during winter was observedevery year but was unlikely to represent an important carbonsource into the region due to its short-term nature. Local speciessuch as T. turbinata, P. crassirostris and O. rigida form amajor component of the copepod assemblage. The high copepoddiversity in the area was caused by the year-round presenceof many local species and the aggregation of different speciesfrom subtropical, tropical, and temperate water masses. Monsoon-drivenwater currents and the Kuroshio Branch Current appeared to maskthe effect of river discharge in the region.