Macrobenthic community structure in the Changjiang Estuary and its adjacent waters in summer

On the basis of data collected in the summer of 2006 from 27 sampling stations in the Changjiang Estuary and its adjacent waters,the ecological characteristics of macrobenthos and the relationship between the macrobenthos and the environmental factors were studied using hierarchical cluster and non-metric multidimensional scaling(MDS).The biomass,abundance,Shannon-Wiener's and Margalef's indices of the macrobenthos were presented.The results showed that a total of 253 macrobenthic species were found in the research region,and most of them belong to mollusks and polychaetes.The dominant species were Cossurella dimorpha,Eocylichna cylindrella,Episiphon kiaochowwanense,Nassarius semiplicatus,Ocstergrenia variabilis and Sternaspis scutata.The average abundance of the macrobenthos was(313.15±233.4) ind./m²,and the average biomass was(15.2±11.2)g/m².The distribution patterns of the abundance and biomass of the macrobenthos were similar.The abundance and biomass in the area close to the estuary were lower than those from the area more distant to the estuary; the central part of the research region had higher abundance and biomass than other parts of the research region.In accordance with the results,four macrobenthic communities with distinct spatial differences were identified.The low abundance and biomass in the area close to the estuary should be caused by the high sedimentation rate.The statistical analysis indicated that the depth is the most important factor affecting the distribution of macrobenthos.