Influence Of Reclamation Projects On The Macrobenthos Of Nanhui And Chongming East Tidal Flats

Yangtze estuary wetland locates at the global ecological hotspot and ecological sensitive area, that with important value of ecosystem services. Along with the rapid development of regional economy in the Yangtze Estuary, the increasing strict contradiction between the limited wetland resources and urban construction land scarcity. Wetland reclamation had becomed the prominent way to get land in the Yangtze Estuary. It has been excessive reclaimed in the Yangtze Estuary recent years and results in a series of ecological problems. For example, Nanhui east tidal flat, one of the continental margin wetland, had become the most frequent, the largest area and the longest time of reclamation in the Yangtze Estuary. The other wetland, Chongming east tidal flat, had also become "wetland reclamation". It is urgent to further study the influence of reclamation on the macrobenthos community and provide the ecological evidence for scientific reclamation in two wetlands.This work using of aquatic animal models and adopts variety of methods, including species composition, density, biomass, dominant species, diversity index and other aspects and combined the historic resources to ascertain the macrobenthos community structure of Nanhui and Chongming east tidal flats present situation and influence of relamation. Based on this study, Salinity was selected an important environmental factor and simulated salinity’s variation after reclamation in the laboratory. The study chose the dominant species of Helice tientsinensis and took a variety of biological methods to study the influence of salinity stress on Helice tientsinensis osmotic regulation. The data obtained form wetland macrobenthos can serve as reclamation on macrobenthos and with dominant theoretical significance and practical application value. Summarized results as follows:1. Reclamation directly influenced the community structure of macrobenthos in Nanhui and Chongming east tidal flats. The species composition of two wetland were decreased significantly after reclamation; Diked tidal flats has higher density and lower biomass in Nanhui east tidal flats, but demonstration area(Diked tidal flats) has lower density and biomass than control area(natural tidal flats) in Chongming east tidal flats; the total number of dominant species reduced significantly; Diked tidal flats’s diversity index was significantly lower than those natural tidal flats; The results of cluster analyses and MDS indicated that community structure of macrobenthos has a big difference between diked tidal flats and natural tidal flats. Salinity, one of the most environmental factors was reduced after reclamation and as well as one of the leading causes thatresults in macrobenthos death.2. Environmental factors of salinity changed (the same problem with above mentioned) after reclamation and it has certain influence on Helice tientsinensis osmotic regulation. Low salt stress and high low stress has obvious effect to enzyme activity assay, gill tissue ultrastructure and gene expression of Helice tientsinensis compared with control group. The damage results from low salt stress was greater to Helice tientsinensis in osmotic regulation compared with those high salt stress. Helice tientsinensis had the capability to adopt itself to a certain salinity the range of 4‰ and 16‰,to keep normal osmotic regulation mechanism and to explain the reason why the population disappearance of Helice tientsinensis after reclamation.