Distribution characteristics of zooplankton in waters around Yangshan Islands in Hangzhou Bay

An oceanographic comprehensive survey was carried out in waters around the area of Yangshan Islands in Hangzhou Bay (30°32′-30°50′N、121°53′-122°17′E) during the months of February, May, August, and November, 2002 representing winter, spring, summer, autumn and winter respectively. The zooplankton samples were collected using zooplankton net of mesh size 0.505mm. The results show that 44 species of zooplankton were identified (excluding 16 species of larvae), in which 15 species were identified dominant species with dominance Y≥0.02. Only Labidocera euchaeta as dominant species appeared in four seasons. The phenomenon of seasonal alteration was evident in dominant species. The seasonal variation of zooplankton biomass in the investigated waters of Hangzhou Bay was clearcut, the order of variation being summer spring winter autumn. In comparison with the data obtained 20 years ago, there was no significant variation in timespatia distribution of zooplankton biomass. The biomass of zooplankton highly distributed in the near shore of Ruchao harbor in the seasons of winter and autumn and around Yangshan Islands in spring and summer. The ecological community, species number and composition of dominant species of zooplankton remained unchanged in the past 20 years, but the dominance (Y) and average abundance of dominant species increased higher than those before. Diversity index (H′) stood at around 2, showing that the community composition and structure of zooplankton were still kept stable.