[Comparison of mesozooplankton communities in North Channel and North Branch of Yangtze River Estuary].

According to the four cruises investigations in the Yangtze River Estuary from May, August and November 2004 and February 2005, and by using species diversity indices, K-dominance curves, and similarity analysis (ANOSIM), the features of mesozooplantkon communities and their dominant species in the North Channel (NC) and North Branch (NB) were analyzed, with the effects of ecological factors, especially water salinity and temperature, on the dominant species and communities in these two waters discussed. The results indicated that the NC was composed of tidal water and oligo-haline water, while the NB was featured by meso-haline or poly-haline water. Consequently, the zooplankton communities in these two waters were significantly different. In spring, the abundance and diversity of the communities were larger in NB than in NC. In NC, Sinocalanus sinicus was the only dominant species; while in NB, there were several dominate species, among which, Labidocera euchaeta was most important. In summer, the diversity of the communities in NC and NB was quite similar, but the species richness and total abundance of zooplankton were less in NC than in NB. The zooplankton in NC was made up of olio-haline communities, and that in NB was composed of brackish species, e.g., Schmackeria poplesia and Tortanus vermiculus. In autumn, similar to those in spring, the abundance and diversity of the communities were larger in NB than in NC. As usual, in NC, S. sinicus was the most important species; while in NB, the zooplankton was composed of neritic community (Paracalanus parvus, P. aculeatus, L. euchaeta, and Calanus sinicus, etc. ). In winter, the species richness and diversity were the lowest, and there were no obvious difference between the zooplankton communities in NC and NB. It was concluded that water salinity, water temperature, and their combination were the key factors determining the characters of the mesozooplanktonic communities. Water temperature mainly affected the seasonal alteration of the dominant species, while water salinity, which was influenced by the interaction between runoff and ocean mass, determined the local mesozooplantkon communities in NC and NB.