TIDALFLAT ECOLOGICAL CHANGES BY TRANSPLANTING SPARTINA ANGLICA AND SPARTINA ALTERNIFLOREA, NORTHERN JIANGSU COAST

In order to evaluate the impact of artificially introduced cord grasses on coastal wetland ecosystem of Jiangsu Province, eastern China, a transection on the upper intertidal zone, 950 m long spanning three types of vegetation covers (i.e. Suaeda salsa, Spartina angilica and Spartina alterniflora flats), was established at Wanggang, Jiangsu, in a multi-disciplinary investigation. In summer and autumn 2003, surficial sediment and plant samples were collected, the bed morphology was surveyed by leveling, and the size of animal burrows (mainly formed by marsh crabs) was measured in the study area. Grain size was analyzed in laboratory, and above ground biomass of the tidal flat plants, and the distribution patterns of the animal burrow sizes were also studied.The bed was covered mainly with silty sediments on all the three types of flats. The sediment was finer on Spartina alterniflora flat which is located in lower part of the transection, than on Suaeda salsa and Spartina angilica flats. Before the cord grasses were introduced, the bottom sediment had a coarsening trend from higher part to lower part of the intertidal zone. Therefore, the presence of the cord grass Spartina angilica favors the accumulation of fine-grained materials and has modified the original sediment distribution of the flat.The above ground biomass of the three different biotic communities shows that the net primary production on Spartina alterniflora flat was the highest, reaching the order of 2×10 2 gC/m 2 in summer and 8×10 2 gC/m 2 in autumn, indicating rapid increase during summer and early autumn. These values were significantly higher than those of the Suaeda salsa and Spartina angilica flats, where the net primary production was in the order of 4×10 1 gC/m 2 in summer and 5×10 1 gC/m 2 in autumn. The growth of the plants on these flats slowed down after July. The facts indicate that the biomass or net primary production on the tidal flat has been enhanced significantly since Spartina alterniflora was transplanted.Non-parameter test of the animal burrow size (mainly crab burrows) suggests that the burrows on the Suaeda salsa flat were significantly different from those on the Spartina angilica and Spartina alterniflora flats, but there was no significant difference between Spartina angilica and Spartina alterniflora flats. In the summer, the burrows on the Suaeda salsa flat were larger but fewer; in the autumn, the burrows were smaller, with a significant increase in number. Thus, the introduction of the cord grasses has changed the burrow sizes and its seasonal variation of the salt-marsh animals. Nevertheless, the relatively stable distribution of the burrows on both Spartina angilica and Spartina alterniflora flats indicates that the marsh crabs could well adapted to the new environment. However, more studies are required to understand the ecosystem structure and functioning in response to marsh vegetation changes.