Community Structure Of Macrozoobenthos And Its Relationship With Environmental Factors In Sanmen Bay

Sanmen Bay is one of the important bays in Zhejiang Province,and macrozoobenthos are the important part of the marine ecosystem.In November 2015(Autumn),and February(Winter),May(Spring)and August(Summer)in 2016,a total of 4 voyages,we collected macrozoobenthic samples as well as sea water and sediment samples and environmental data in Sanmen Bay.According to all the data,we studied the status and dynamic changes of the macrozoobenthos community and its relationship with environmental factors,and evaluated the water quality and sediment quality of Sanmen Bay.Four biological indexes,i.e.AMBI,M-AMBI,BENTIX and MPI,were used for the first time to evaluate the environmental quality of Sanmen Bay,and their sensitivity were also detected along with Shannon's diversity index.The results showed that,a total of 119 species of epi-macrozoobenthos collected by Agassiz trawl were identified.The main groups were fishes,crustaceans and molluscs,accounting for 79.0% of the total number of epi-macrozoobenthic species in Sanmen Bay.The dominant species of epi-macrozoobenthos throughout the year were Leptochela gracilis,Hyperacanthomysis longirostris and Amblychaeturichthys hexanema.The dominant species changed significantly in different seasons.The annual average biomass and density were 0.025 g·m-2 and 0.070 ind.·m-2,respectively.The Shannon's diversity index of epi-macrozoobenthos in Sanmen Bay varied from 2.21 to 3.18,the Margalef's species richness index varied from 3.25 to 3.78,and the Pielou's evenness index varied from 0.53 to 0.79.A total of 79 species of endo-macrozoobenthos collected by Van Veen grab were identified.The main groups were crustaceans,molluscs and polychaetes,accounting for 86.08% of the total number of endo-macrozoobenthic species in Sanmen Bay.The dominant species of endo-macrozoobenthos collected throughout the year were Sternaspis sculata,Amaeana occidentalis and Mediomastus californiensis.The annual average biomass and density were 15.02 g· m-2 and 201.75 ind.· m-2,respectively.The Shannon's diversity index of endo-macrozoobenthos in Sanmen Bay varied from 1.89 to 3.02,the Margalef's species richness index varied from 5.23 to 8.58,and the Pielou's evenness index varied from 0.56 to 0.87.The results of Abundance-biomass curve(ABC)analysis showed that,the epi-macrozoobenthos community was moderately disturbed in spring and winter,and slightly disturbed in summer and autumn.The endo-macrozoobenthos community was undisturbed in spring,summer and autumn,and slightly disturbed in winter.The results of canonical correspondence analysis(CCA)showed that water depth,bottom water temperature,salinity and p H were the most important environmental factors affecting epi-macrozoobenthos community.The bottom water temperature,salinity,dissolved oxygen and particle size were the most important environmental factors affecting endo-macrozoobenthos community in the Sanmen Bay.Based on the results of surveys and analysis of water quality and sediment of the Sanmen Bay,combined with the marine environmental function zoning,we evaluated the environmental quality status of the Sanmen Bay,and analyzed the eutrophication levels of the sea water,and accumulation levels and potential ecological risks of heavy metals.The results showed that,the values of environmental factors examined in the sea water were corresponding to the sea water quality standard except some values of dissolved inorganic nitrogen(DIN),dissolved inorganic phosphate(DIP),p H and chemical oxygen consumption(COD).Values of heavy metal content examined in the sediment all met the standards,showing good condition of the seabed.Values of the eutrophication index in different seasons were all greater than 1,showing high eutrophication level in the sea water.Seasonal values of the potential ecological risk index of heavy metals were far less than 150,indicating that the potential ecological risk was low in the Sanmen Bay.The causes of sea water eutrophication were complex,and more comprehensive surveys and analysis were needed in the future.Based on the endo-macrozoobenthos data in the Sanmen Bay,we calculated the values of 4 benthic biological indexes,the AZTI's Marine Biotic Index(AMBI),Multivariate-AMBI(M-AMBI),Macrozoobenthos Pollution Index(MPI)and BENTIX, and Shannon Diversity Index(H),and evaluated the environmental quality status and sensitivity of all the biological indexes in the Sanmen Bay.The results showed that the Shannon diversity index is more appropriate in the Sanmen Bay than the other four indexes,while the pollution degree obtained by the four biological indexes is relatively lighter.