| Dongtan of Chongming Island is a wetland of international importance, locatedat the estuary of the Yangtze River, which has been designated as a natural reserve forwaterbirds in Shanghai City. Since the middle of 1990s, Spartina alterniflora, an alienplant, has established successfully at Dongtan of Chongming by natural dispersal andintentional introductions, and spread and swamped rapidly new areas where it was notplanted. In order to evaluate the ecological impacts of S. alterniflora invasions on theDongtan wetland ecosystems of Chongming Island, we focused on communitycomposition in Dongtan wetland ecosystems. We mainly studied community changesof native plant (Scirpus mariqueter), benthic macroinvertebrates and shorebirdscaused by S. alterniflora invasions. The major findings are summarized as follows: 1. Comparing the tolerance of S. alterniflora with S. mariqueter for salt stress,we found that S. alterniflora could tolerate wider range of salinity than could S.mariqueter. S. alterniflora could grow and reproduce as usual under the condition ofsoil salinity from 0 ppt to 32 ppt, while S. mqriqueter could not grow and reproducenormally when the soil salinity is higher than 16 ppt. The potential distribution area ofS. alterniflora may be larger than that of S. mariqueter in Dongtan tidelands, and thedistributions of both plants were overlapped in some areas, suggesting that there is alack of refuge in Dongtan for S. mariqueter as S. alterniflora competitively exclude it.S. alterniflora adapts itself to the Dongtan wetland ecosystems , and its total areas wasover 1000 hm2. 2. The relative competitive ability of S. alterniflora and S. mariqueter had beenevaluated with a pot experiment at the soil salinity of 3~4 ppt, which is comparable tothat at Dongtan. We found that the interspecific RNE (Relative Neighbour Effect)index of S. alterniflora was significantly higher than the intraspecific RNE, but therelationship was inversed for S. mariqueter. The interspecific RNE index of S.alterniflora was significantly higher than that of S. mariqueter. 3. In May 2001, S. alterniflora was transplanted to the inner zone of S.mariqueter community by the local government for rapid sediment accretion. In order ivto determine how introduced S. alterniflora affects S. mariqueter population dynamics,field work were conducted at Dongtan from March 2002 to November 2003. Theresults obtained here show that S. alterniflora had strong competitive effects on S.mariqueter, and that the introduction of S. alterniflora to S. mariqueter communityresulted in a significant decrease of S. mariqueter's abundance, coverage, seed andfresh corm output after two growing seasons. 4. Based on soil cores sampled (sampled at October 2002, January, April andJuly 2003 respectively) at the tidelands of northern Dongtan, we compared thecommunity structures of benthic macroinvertebrates (except for crabs) in S.alterniflora community with that in S. mariqueter community. We identified a total of25 species, including Nemertinea (1 species), Polychaeta (8), Oligochaeta (1),Gastropoda (8), Lamellibranchia (3), Crustacea (2) and Insecta (2). Meanmacroinvertebrate density tended to be lower in S. alterniflora (3119 individual/m2)than that in S. mariqueter community (3459 individual /m2), but the overall effect ofplant community type on density was not significant. However, the densities of somecommon species (mean density > 100 individual /m2 in at least one plant communitytype) were significantly different between S. alterniflora and S. mariquetercommunities. For example, the density of Assiminea violacea was significantlygreater in S. alterniflora community than that in S. mariqueter community, but thedensities of A. lutea, Stenothyra glabra, Cerithidea sinensis and Glaucomya chinensiswere significantly lower in S. alterniflora community than those in S. mariquetercommunity. The dominant species of macroin...
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