Effects of Spartina alterniflora Invasions on the Benthic Macro-Onvertebrates Community at Dongtan of Chongming Salt Marsh, the Yangtze River Estuary

Spartina alterniflora , an alien invasive plant, has been displacing rapidly Scirpus mariqueter which is a dominant plant at Dongtan of Chongming salt marsh. In order to understand the responses of tidal marsh benthic macro invertebrates assemblages to the conversion of S. mariqueter marshes to marshes dominated by the invasive S. alterniflora , we used core sampling (sampled at October 2002, January, April and July 2003 respectively) to compare the density, diversity, and composition of the intertidal benthic macro invertebrates (except for crabs) of S. alterniflora marsh and adjacent remnant S. mariqueter marsh at the tidelands of the northern Dongtan. The results indicated that mean macroinvertebrate density tended to be lower in S. alterniflora (3 119 individual/m 2) than that in S. mariqueter community (3459 individual /m 2), but the overall effect of plant community type on density was not significant. However, the densities of some common species (mean density 100 individual /m 2 in one plant community type, at least) were significantly different between S. alterniflora and S. mariqueter communities. The dominant species of macro invertebrate community were Assiminea violacea and Heteromastus filiforms in S. alterniflora and S. mariqueter community. Mean species richness, Shannon Wiener index, evenness index were significantly lower in S. alterniflora community than those in S. mariqueter community, and Simpson’s Dominance index was inversed. The proportion of detritivore was significantly greater in S. alterniflora community than that in S. mariqueter community, and the proportions of herbivore and suspensivore were significantly lower in S. alterniflora community than those in S. mariqueter community. Overall, the invasions of S. alterniflora in S. mariqueter community at Dongtan significantly decreased the species diversity of macroinvertebrates, and altered trophic group structure of macro invertebrates community. These changes of vegetation, such as the height, density, coverage and biomass, might be the major factor influencing the community structure of macro invertebrates.