Does invasion of Spartina alterniflora alter microhabitats and benthic communities of salt marshes in Yangtze River estuary?

Smooth cordgrass Spartina alterniflora has rapidly spread in salt marshes of Yangtze River estuary. However, there is no consistent pattern on the effects of S. alterniflora invasions on microhabitats and benthic communities. The study first compared vegetation, water velocity, sediment deposition rate, sediment properties and benthic communities between invasive S. alterniflora and native Scirpus mariqueter patches using a pair-wise sampling design at 3 sites (Dongtan, Jiuduansha and Nanhui) in four seasons. The stands of S. alterniflora exhibited taller and less dense shoots, greater aboveground biomass and longer phenological phase than did S. mariqueter. S. alterniflora marshes had significantly lower water velocity, greater sediment deposition rates and higher light attenuation relative to S. mariqueter habitats. In general, sediment temperature, salinity, porosity, organic carbon content and microalgal biomass (Chla) did not significantly differ between invaded and uninvaded habitats at any of 3 sites. Thirty-four of 37 macrofauna species recorded did not exhibit density differences between habitat types. Limited influences on macrofauna were evident only at Dongtan where S. alterniflora marshes had significantly greater gastropod densities in the autumn. In 8 of 12 observations, benthic community structure did not differ between invaded and uninvaded habitats. It was concluded that the differences in physical structure were not enough to significantly change sediment properties, macrofaunal density and community structure.