The seasonal and annual variation of zooplankton community was investigated at a fixed station in the coastal waters of the Straits of Malacca. Sampling was carried out monthly by vertical hauls of a 140μm plankton net from June 2002 to May 2004. Zooplankton were identified and grouped into respective taxonomic groups and 23 genera of copepods were identified. Copepods dominated the zooplankton community and among them, the genera Acartia, Acrocalanus, Paracalanus, Euterpina, Corycaeus and Oithona were dominant. They accounted for approximately 90% of the total copepod population throughout the year, emphasizing the importance of small species in tropical zooplankton communities. Zooplankton biomass generally peaked at the beginning of each monsoon and gradually decreased toward the intermonsoon periods. Biomass seemed to increase with increasing ambient chlorophyll-a concentration. Cluster analysis of zooplankton abundance showed two distinct groups relative to the SW and NE monsoons. The population of Acartia pacifica and A. spinicauda, the two most abundant species in the genus Acartia (>90%), showed alternating peaks throughout the year, with A. pacifica appearing primarily during the NE monsoon and A. spinicauda, during the SW monsoon. The presence of the effect of monsoon on zooplankton community in tropical waters is suggested
