The Study On Relationship Between Macrobenthos Community And Spartina Alterniflora Salt Marsh In The Yangtze Estuary

In this paper, we took the tidal flats in the Yangtze Estuary as a case study. The community structure and biodiversity of macrobenthos in the exotic Spartina alterniflora salt marsh were studied. The relationship between environmental factors and macrobenthos were also analyzed. The ecosystem services value of S. alterniflora salt marsh was evaluated in the end.This study concentrated at the influence on estuarine macrobenthos impacted by S. alterniflora salt marsh, investigated the change of species composition, abundance and diversity of macrobenthos after the introduction of S. alterniflora to the Yangtze Estuary. The ecological effects of S. alterniflora salt marsh were analyzed. This study could deepen the study on estuarine ecosystem and process. It also helped to evaluate S. alterniflora, and to supply scientific foundation of applying S. alterniflora for ecological restoration.Major conclusions were as follow:1 The species abundance and diversity of macrobenthos in S. alterniflora salt marsh was at the mean level among different habitats. Species composition of macrobenthos were strongly related to sediment grain size, elevation and vegetation (P<0.05). Only 3 species were recorded in sand flat while abundance and diversity were lowest among several habitats. Macrobenthos in Salix matsudana zone turned to be terricolous and differed from others because of elevation. Macrobenthos in mud flat was similar with which in salt marsh. The study demonstrated further that macrobenthos in the tidal flat wetlands of Yangtze Estuary were mainly affected by sediment, elevation and vegetation.. Macrobenthos in S. alterniflora and Phragmites australis salt marshes had the highest similarity (60%).2 Along the environmental gradient, species numbers and diversity of macrobenthos in S. alterniflora salt marsh presented a trend of increasing gradually from the upper to the lower region of the Yangtze Estuary. 21 species were identified. Assiminea sp., Notomastus latericeus, Cerithidea largillierl, Glauconome chinensi, Gammaridae sp. were the dominant species. Functional groups were mostly composed ofdetritivorous group and phytohagous group. The average density of all macrobenthos was 650.5±719.2ind./m². High value of standard deviation of density was a result of abundant Assiminea sp. at BH. The density and diversity were the highest in summer while lowest in winter. The mean biomass of macrobenthos was 20.8±6.1 g/m². Seasonal dynamic of biomass was: summer > autumn > spring > winter. The BIO-ENV analysis showed that mean grain size of sediment and height of Spartina were the major factors which affected the abundance of macrobenthos in S. alterniflora salt marsh..3 Abundance and diversity of macrobenthos was higher in S. alterniflora salt marsh which had developed after a longer time than which a shorter time. Community structure and diversity of macrobenthos were closely related to the development of salt marsh. After being introduced into Yangtze Estuary, S. alterniflora influenced the macrobenthos by competing with Phragmites australis and changing the hydro-geological conditions. In the beginning of foundation of S. alterniflora salt marsh, macrobenthos were mainly composed of gastropod. The abundance and diversity were at a lower level while species richness (d=2.18) and diversity (H'=2.19) were both lower than in P. australis salt marsh (d=2.61, H'=2.29). With the passage of time, species numbers of polychaeta increased (from 3 to 6) while species numbers and abundance of macrobenthos increased. A new pattern of macrobenthos was formed. Species richness (d=2.70) and diversity (H'=2.48) of macrobenthos were higher in S. alterniflora salt marsh than in P. australis salt marsh (d=2.19, H'=2.09). But it would take a long period for the foundation of new community.4 8 classes of ecosystem services value of S. alterniflora salt marsh in Yangtze Estuary were analyzed. The value was 317 570 000 Yuan per year. The value per unit area was 697,000 6.97Yuan ha^-1.yr^-1, which was 275% more than the average value in the Yangtze Estuary. The services value from more to less was the value of land forming, atmosphere regulation, material production, wave dissipating, science culture, nutrient cycle, environment purification and biodiversity. The value of land forming and atmosphere were up to 71% of the total value. The ecosystem service values of S. alterniflora salt marshes per unit area were higher than or equal to the mean value in the Yangtze Estuary. This showed that S. alterniflora could be used as engineering species for ecological restoration. The value per unit area of land forming, material production and atmosphere regulation were higher in the Yangtze Estuary than in Hangzhou bay.While the value per unit area of environment purification and biodiversity and atmosphere regulations were higher in Hangzhou bay. This was resulted by difference of economic geography and biomass of S. alterniflora between two areas. Taking different use target into account, ecosystem services of S. alterniflora salt marsh might have different value. S. alterniflora salt marsh should be dealt with different ecosystem management ways.In conclusion, the abundance and diversity of macrobenthos in S. alterniflora salt marsh was at the mean level in the Yangtze Estuary, and presented a trend of increasing gradually from the upper to the lower region along the environmental gradient. The abundance was affected by mean grain size of sediment and height of Spartina. In the beginning of foundation of S. alterniflora salt marsh, the abundance and diversity of macrobenthos were at a lower level, especial for the crabs. With the time went by, a new pattern of macrobenthos community formed. The abundance and diversity increased gradually, even higher than in P. australis salt marsh. S. alterniflora salt marsh had a high value of ecosystem services. But we should envisage the negative effect impacted by S. alterniflora. It grows quickly, competes with the native species strongly and changes the habitats and biodiversity if the local salt marshes, especially in some mud flats fit for shellfish culture. S. alterniflora salt marsh decreased the habitats for shellfish and wetland birds. So, we should evaluate S. alterniflora in a dialectic opinion. S. alterniflora salt marsh should be dealt with different ecosystem management ways. We should control S. alterniflora in aquaculture area and wetland bird's habitats and develop S. alterniflora salt marsh in a scientific model in other areas.