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Secondary productivity is an important indicator of the variation of the structure,function and stability of an ecosystem.The goal of this study was to test the hypothesis mangrove habitat promotes the production of macrobenthos and increases ecosystem stability under the influence of urbanization.We collected samples monthly in four basic habitats,Phragmites communis reed beds with frequently inundated soil(reed beds),gei wai ponds,mudflats,and mangrove habitat,and analyzed the secondary productivity of macrobenthos,the production/biomass(P/B) ratio,and the dominance and the diversity of macrobenthos from January to December of 2010.The results show secondary productivity in these four habitats varied widely.The secondary productivity in reed beds,gei wai ponds,mudflats,and mangrove habitat was 6.81,147.50,74.70,and 105.78 g · m-2 × a-1,respectively;and the P/B ratios were 1.10,1.53,1.41,and 3.58 a-1,respectively.Secondary productivity in the mangrove habitat was only lower than in the gei wai ponds,while mangroves had the highest P/B ratio,meaning the turnover rate was fastest.The seasonal variation of secondary productivity among the four habitats also varied;gei wai ponds had the highest secondary productivity and it remained relatively stable all year.The other three habitats had the same trend with secondary productivity high in spring and autumn,and lowest in summer.The seasonal variation of the P/B ratio in geiwai ponds and reed beds was relatively stable,while the mangrove and mudflat habitats had the same trend with higher P/B in spring and autumn,and lowest in summer.The species composition and dominance in the four habitats were significantly different seasonally.Reed beds were dominated by two gastropods,Cerithidea cingulata in spring and summer,and Melanoides tuberculata in winter.The gastropod Sermyla riqueti dominated gei wei ponds all year.The dominant species of mudflats were Nereis glandicincta in summer,S.riqueti in autumn,S.riqueti and Cipangopaludina chinensis in winter.Mangroves were dominated by Ellobium aurismidae in summer and autumn and Uca urvillei in winter.The macrobenthic diversity also varied seasonally in the four habitats.The level of biodiversity in the four habitats was mangrove mudflats gei wai ponds reed beds,with mangroves having the highest diversity in all four seasons.The seasonal variation of macrobenthic diversity in gei wai ponds and reed beds was relatively stable,while the mangrove and mudflat habitats had the same trend with lowest biodiversity in summer and higher in autumn,that may be resulted by tropical storm.The increase of macrobenthic productivity,the P/B ratios and biodiversity in the autum than in the summer is bigest in mangrove habitat.Based on the analysis of the macrobenthic productivity,the P/B ratios,and the seasonal variation of the macrobenthic dominance and diversity,we concluded the mangrove habitat had the highest biodiversity,ecosystem resistance to change and resilience,and conclude the mangrove ecosystem was the most stable ecosystem.Above all,the mangrove habitats played a significant role in promoting species diversity for macrobenthos,improving the turnover rate,and in increasing both ecosystem nutrient retention and stability which reduced urbanization threats to the health of the ecosystem. |
