The spatial pattern of macrozoobenthic communities in the tidal wetlands of Shanghai City

The macrozoobenthos were sampled in six tidal wetlands of Shanghai City (Chongming Dongtan, Chongming Beitan, Jiuduansha, Qingcaosha, Nanhui Biantan and the northern bank of Hangzhou Bay) along 27 transects from the high to low intertidal during 2004-2006. A total of 112 species was recorded. Crustaceans, mollusks and annelids were the dominant taxonomic groups and accounted for approximately 51.8%, 22.3% and 18.8% of the total number of species, respectively. The macrozoobenthic biomass in six tidal wetlands showed a consistent spatial distribution pattern, namely high intertidal > middle intertidal > low intertidal. The relative contributions of several taxonomic groups to the total biomass varied within and among the six tidal wetlands. Crustaceans accounted for about 51% to 97% of the total biomass of macrozoobenthic communities. Mollusks accounted for 2% to 48% of the total biomass and increased from the high to low intertidal in Dongtan and Jiuduansha wetland. There is no consistent spatial pattern for the total density of macrozoobenthic community in the six tidal wetlands. In three of them (Chongming Dongtan, Chongming Beitan and Jiuduansha), the greatest density of macrozoobenthic community appeared in the middle intertidal, with the lowest in the low intertidal. The relative contributions of major taxonomic groups to the total density also varied within and among the six tidal wetlands. In Chongming Dongtan, Jiuduansha and the northern bank of Hangzhou Bay, mollusks dominated the macrozoobenthic communities, accounted for between 66% and 77% of the total density. But in the other three wetlands (Chongming Beitan, Qingcaosha and Nanhui biantan), crustaceans were the dominant group. The mean macrozoobenthic biomass in the tidal wetlands sharply increased from the early 1980s and 1990s to the mid 2000s. The macrozoobenthic community in the tidal wetlands had shifted from the mollusk-dominated to crustaceans-dominated , which possibly resulted from the serious anthropologic disturbance (over-harvest, environmental pollution and biological accretion). The alternation in the community structure possibly influenced the biological production and ecological service value, decreased the quality of bird prey and nektons, and accelerated the biogeochemistry process of nutrients in the tidal wetlands.