Distribution pattern of zooplankton in the Oujiang Estuary during summer and autumn

Based on the zooplankton samples from stations in the Oujiang Estuary during June and September 2007, the spatial and temporal distribution characteristics of the abundance and biomass of zooplankton in the area were studied, moreover, the relationships between the environmental factors and zooplankton were discussed. Then the dominant species of each season was identified and the contribution of the abundance of these dominant species to total abundance was analyzed. The results indicate an obvious succession of dominant species. Centropages dorsispinatus, Acartia paci? ca and Sagitta en? ata were the primary dominant species in summer( June), however, Paracalanus aculeatus, Acartia pacifica and Paracalanus crassirostris were the major dominant species in autumn( September). The average biomass of zooplankton was 82.05 mg·m-3 in summer, and 649.1 mg· m-3 in autumn. Moreover, the abundance were 47.00 ind·m-3 in summer and 298.30 ind·m-3 in autumn. Both the biomass and abundance of zooplankton were higher in northern water than those in southern water. In addition, the distribution patterns of biomass and abundance were similar. The regional variations of dominant species were determined by the seasonal change of runoff, the split ratio between north branch and south branch, the strength of Taiwan warm current and the Zhemin coastal current. Moreover, temperature and salinity were the essential factors to determine the seasonal changes of zooplanktonic abundance, particular the salinity which is the key factor to affect the horizontal distribution and abundance of zooplankton. In short, the dynamics of the abundance of total zooplankton is attributed to the changes of dominant species.