Responses of zooplankton community to changes in water masses in the Sansha Bay

For a comprehensive understanding of the interactive relationships of zooplankton ecogroups and their response to the changing water masses, the species composition and horizontal distribution of zooplankton in the Sansha Bay was analyzed to study the effect of water masses on the salinity adaptation of zooplankton. Distribution of zooplankton were investigated from samples collected from 10 stations during 5 oceanographic cruises in April, May, June, August and October in the Sansha Bay. All together 71 species were identified, including 36 nearshore species and 34 offshore species. The result showed significant differences in structures of ecogroups among months. In April and May, the nearshore species accounted for more than 97% of the total zooplankton abundances for all stations. The ambient water was influenced by the continental fresh runoff and the Zhemin Coastal Current, both with low salinity. From June to October, the abundance percentage of nearshore species fluctuated between 40.07% and 82.88%. There were significant differences between the two characteristic zooplankton communities in the northwestern and southeastern parts of the Bay, probably due to the effect of the Taiwan Warm Current. The northwestern part was characterized by high proportions of nearshore species in both number and abundance. The outer Bay of the southeastern part was characterized by relatively high proportions of offshore species in number and abundance. Our research revealed that the salinity adaptation and the temporal and spatial distribution of zooplankton are closely related to the currents changing with season.