An in situ study on the macrobenthic fauna community in Scirpus mariqueter zone of Chongming Dongtan in the Yangtze Estuary was carried out from April to October in 2006. The macrobenthic fauna and vegetation were sampled using a quadrat method synchronously every month and samples were analysed in the laboratory including species identification individual count and biomass measure (Dry weight). Then biodiversity cluster and multidimensional scaling analyses were carried out. The results proved that during the growing seasons the abundance and the biomass of the macrobenthic fauna community in the
Scirpus mariqueter
zone had a trend of increasing while there was still some fluctuation between different months. The abundance arrived at a peak of 1536 ind/m
2 on average in September，and the biomass arrived at a peak level of 21.60 g/m
2 (DW) on average in October. The composition abundance and biomass of the dominant group had different characteristics in different months the species of Lamellibranchia only had the dominant characteristics in some periods. The track of the species' monthly variation had a similar shape to character V and the low point arrived in August. Due to the temporal lag between the change in species number and the variation of individual number distribution among different species，the fluctuation of the Shannon-Wiener index value and Pielou evenness index value appeared to be a little later than that of the species number regardless of whether it was a peak or low point. The species numbers had a low point in May and the biodiversity indices got the lowest point in June. The synthesis of different factors including hydrological dynamics and the vegetation led to the monthly variation in the macrobenthic fauna community. And during different periods different factors had various impacts on the community. Usually they directly affected the species composition and abundance which in turn changed the biodiversity and biomass characteristics of the community.
