The biodiversity of marobenthos of intertidal zone on Chongming island in summer

Chongming Island (31°25′N-31°50′N, 121°10′E-122°00′E) is the largest alluvion of China and situates in the Yangtze estuary. We investigated the Summer macrobenthos species diversity in the Chongming Island intertidal zone and the species distribution trend. Study materials were collected in June 2006 for qualitative and quantitative investigation from 21 sections in the Chongming Island intertidal zone. The Shannon-Wiener index, Pielou's eveness index, Simpson's diversity index, clustering analysis and MDS were applied to analyse the data of community structure, species assemblages, dominant species and macrobenthos abundance. In this investigation, 63 macrobenthos species were obtained, of which 29 species are crustacean (46.03%), 20 species are mollusca (31.75%), 10 species belong to annelida (15.87%), 2 species are dermesal fishes and 2 other species. Among dominant species were: Sesarma dehaani, Helice tientsinensis, Ilyrplax deschampsi, Cerithidea sinensis, Assiminea violacea, Assiminea latericea, Stenothyia glabra, Heteromastus filiformis. The average marozoobenthos abundance was 138.28 ind/m², and the biomass was 79. 11g/m². According to the clustering analysis and MDS results, the sections were divided into limnetic groups, brachish groups and hyperhaline groups situated respectively at the south, north and east (including west) of Chongming Island. Shannon-Weiner index H′=1.85±0.528 (range 0.946-2.783), Pielou index J′ =0.306±0.098 (0.142-0.489), Simpson diversity index D=0.622±0.141 (0.303-0.797). The difference of species composition, biomass, abundance and diversity indexes between the sections are caused by salinity, substrate and artificial activities. Compared with the previous data, the total species and diversity index didn't change much during recent years, while species composition changed. The abundance and the biomass deceased. The slowing of diking wetland facilitates the biodiversity of marobenthos to convalesce in the intertidal zone. Affected by artificial activities, the runoff of Yangtze River and other factors, the previously dominant species are no longer dominant, and their abundace and distribution area is descreasing. Affected species include Corbicula fluminea, Moerella iridescens, Rissoina sp., Capitella capitata, and Tylorrhynchus heterochaetus.