| Jiuduansha wetland is a new allusion of the Yangtze estuary. In spring (April), summer (July), autumn (October) and winter (December) of 2005, we investigated the macrobenthic species diversity and distribution trend in the Jiuduansha wetland. Study materials were collected for qualitative and quantitative investigation from 9 sections in the Jiudusnsha wetland intertidal zone. Along each section three sites were sampled from the high to the low tidal zone.In this investigation, 83 species of macrobenthos were obtained. The average diversity and biomass were 442.94 Ind·m-2 and 40.78 g·m-2 respectively. These species belong to 4 phylum, 41 families, 57 genus, of which 43 species are crustacean (51.81%), 19 species are mollusk (22.89%), 12 species are annelid (14.56%), and 3 other species (3.61%). 65 euryhaline species are dominant, which take 78.31% among the total, however, only 18 limonitic species were obtained, which take 78.31%.Among dominant species were: Ilyrplax deschampsi, Glauconome chinensis, Bellamya purificata, Assiminea violacea, A. latericea, A. lutea, Corbicula fluminea, Potamocorbula ustulata, and Heteromastus filiformis. 10 species with high IRI were: Ilyrplax deschampsi, Glaucomya chinensis, Helice tidentsinensis, Potamocorbula ustulata, Corbicula fluminea, Assiminea lutea, Bellamya purifcata, Heteromastus filiformis, Sesarma deihaani, Cerithidea sinensis.Macrobenthos in Jiuduansha tidal zone were distributed as communities. Seven macrobenthic communities were found, in which 3 communities were distributed in high tidal zone, 3 communities in middle tidal zone, and one appeared in low tidal zone. The communities are Talorchesti sp. community, Serarma denaani& Helice tridensinensis community, Serarma plicata community, Ilyrplax deschampsi& Assiminea sp. community, Glauconome chinensis& Heteromastus filiformis community, Potamocorbula ustulata, Corbicula fluminea& Nephys oligobranchia community, Macrophthalmus dilatatum& Bullacta exarata community in turn.The most macrobenthic species number was in summer (65 species), less in spring (54 species) and the least in spring and winter (51 species). Accroding to the distribution, 27 species of macrobenthos were in high tidal zone, 56 species in middle tidal zone, 59species in low tidal zone, and 37species in creeks.The most abundance and biomass were in autumn, less in summer and the least in spring and winter; the highest diversity index was in winter, lower in summer and the lowest in spring and winter. Along the altitude, the highest average value of abundance and biomass were in the middle tidal zone, lower in high tidal zone, and lowest in low tidal zone. Abundance, diversity indexes increased from west to east, biomass did not display obvious regularity.The distribution of macrobenthos was mainly affected by the altitude, sediment composition, salinity, and hydrologic disturbance.The species records in this investigation were doubled of previous data. More than 40 species without previous record were obtained, while 3 species with previous record species were not obtained in this survey. Orbinia dicrochaeta and Talorchesti sp. were never found in Yangtze estuary before this investigation. The abundance did not change much compared with previous data, while biomass and diversity index increased. It is concluded that succession, intertidal area expansion, strengthened protection and improved sampling lead to collect more species of macrobenthos than before.Macrobenthic communities are threatened by three main factors. First, the decreasing of runoff and sediment of Yangtze River corrode the wetland and also make sea water infall in the wetland, which decrease the habitat area of the macrobenthos. Second, the invasion of Spartina alterniflora changes the structure of sediment. Species of bivalvia was largely affected, like Glaucomya chinensis etc. Third, the overload fishing makes the quantity of high valued macrobenthos decrease. According to this situation, we propose to limit the fishing and exploiting in the Jiuduansha wetland, for the maintenance of its ecology and as well for the acquirement of greatest social and economic value in long term.
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