Distribution pattern of zooplankton in the south part of Hangzhou bay during spring and autumn in relation to main environmental factors

To understand the community structure and distribution pattern of zooplankton in the south part of Hangzhou Bay and its response to main environmental factors in different seasons, two oceanographic comprehensive surveys were carried out during the September of 2011 (autumn) and May of 2012 (spring). An obvious seasonal variation was found in species composition of zooplankton. In total, 18 species from 8 groups were identified in spring with Tortanus ver-miculus, Sinocalanus sinensis, Calanus sinicus, and Acanthomysis brevirostris being the dominant species, and 25 species from 7 groups were identified in autumn with Labidocera sinilobata, Sag-itta bedoti, Labidocera euchaeta, and Pontella spinicauda being the dominant species. The Shannon diversity index of zooplankton was higher in autumn (1. 60) than in spring (1. 56), while the average biomass and abundance in autumn (580. 58 mg • m^-3 and 578. 88 ind • m^-3) were significantly higher than those in spring (61. 82 mg • m^-3 and 41. 61 ind • m^-3). The distribution patterns of biomass and abundance were mainly determined by the dominant species, which was related to ocean currents. In spring, both the biomass and the abundance increased graduallyfrom outside the bay to inshore. In autumn, the biomass and the abundance increased from outside the bay to inshore and eastern area outside the bay. The correlation between community structure of zooplankton and environmental variables, calculated by the stepwise regression analysis, indicated that temperature and salinity were the two most important factors influencing the distribution pattern of zooplankton in the south part of Hangzhou Bay.