The impacts of biotic and abiotic interaction on the spatial pattern of salt marshes in the Yangtze Estuary, China

Over the past 20 years, S. alterniflora, as an exotic species, has invaded into large areas covered by the native salt-marsh vegetation in the Yangtze Estuary. The original spatial pattern “mudflat - S. mariqueter - P. australis” pattern in the Yangtze Estuary was disturbed due to S. alterniflora invasion and shifted to three types, i.e. original “mudflat - S. mariqueter - P. australis” pattern, new “mudflat - S. alterniflora - P. australis” pattern and transitional “mudflat - S. mariqueter - S. alterniflora - P. australis” pattern. Taking the Chongming Dongtan wetlands in the Yangtze Estuary as a study area, we examined inundation, sedimentary dynamic and hydrodynamic regimes to investigate their impacts on salt-marsh establishment and pattern shifts in coastal wetland ecosystem. The results showed that salt-marsh survival and growth significantly differed under inundation stress on different elevations. The survival thresholds of habitat elevation and inundation duration which determine salt-marsh establishment were identified as 1.9 m and 16 h day⁻¹for S. mariqueter, 2.5 m and 11 h day⁻¹ for S. alterniflora, and 2.9 m and 9 h day⁻¹for P. australis. Both accretion/erosion dynamics and wave energy significantly differed among three types of advancing front, which further indicated that establishment and spatial pattern of salt-marsh were also greatly dependent on sedimentation dynamics and hydrodynamic regimes. Our study indicated S. alterniflora had sustainable competitive advantages, which might become aggressive and gradually replace S. mariqueter and P. australis in the future. Therefore, measures protecting native species should be strengthened and the impacts of invasive species on native ecosystem should be evaluated from more objective perspectives.