Biodiversity And Comniunity Structure Of Acrobenthos In The Yellow Sea

Over the past few decades, the ecological environment in the Yellow Sea haschanged greatly under the impact of global climate change and anthropogenicactivities. The biodiversity and community structure of macrobenthos in the YellowSea were studied in this thesis.Both quantitative and qualitative (grab and trawl) data based on soft-sedimentmacrobenthos in1992and in2007were used to study and compare the composition,distribution, abundance and biomass. The biodiversity was measured at three differentscales: α-diversity, β-diversity and γ-diversity. The agglomerative classification(CLUSTER) and multidimensional scaling (MDS) methods were applied to identifythe macrobenthic communities. The structures of these communities were comparedwith characteristic species designated communities which were sampled nearly50years ago. Multivariate methods were used to detect the how species distributions andcommunities' classification related to environmental variables.A total of142species were sampled from the28quantitative grab sites of theSouth Yellow Sea in1992, and267species from58sites of the Yellow Sea in2007.The average abundance and biomass were175.93ind/m2and15.23g/m2, respectivelyin1992, and340.95ind/m2and25.64g/m2in2007. The abundance and biomass ofeach site were related significantly. Species range size within the study area waspositively related to local abundance of the dominant taxonomic groups. Nosignificant differences of number of species, abundance and biomass were foundbetween the two surveys.Qualitative trawl sampled148species from19sites in1992and311speciesfrom32sites in2007. Although the number of species in site in2007wassignificantly higher than in1992, the number of individuals was not obviouslydifferent.The measurements of α-diversity were highly variable. No significant differencesof these indices were between the two surveys. Two diversity indices, the exponentiated form of the Shannon-Wiener index (ExpH') and the reciprocal ofSimpson's index (1/D), and two evenness indices, Pielou's evenness (J') andSmith-Wilson index (Evar) were recommended for measuring of macrobenthicdiversity.The species richness in1992estimated by the Chao1, Chao2and ICE methodwas142,204.68and229.06, respectively and in2007was267,403.1and407.5,respectively. The randomized numbers of polychaetes and other species in1992werelow than in2007. The numbers of molluscs, crustaceans and echinoderms were almostthe same.The overall βwfor all taxonomic groups pooled was9.68in1992, and12.82forcrustaceans,10.67for molluscs,8.07for polychaetes and8.33for echinoderms. Thenumber of shared species ranged0-11, complementarity (biotic distinctness) ranged0.5-1and Bray–Curtis similarity ranged0-64%. The overall βwfor all taxonomicgroups pooled was16.8in2007, and25.12for crustaceans,14.26for molluscs,14.23for polychaetes and12.96for echinoderms. The number of shared species ranged0-13,complementarity (biotic distinctness) ranged0.556-1and Bray–Curtis similarityranged0-58.3%. Change in environmental variables and spatial distance between siteshad a stronge effect on β-diversity.Seven infaunal clusters and four epifaunal clusters were identified in1992. Theseclusters were classified into three groups of communities: The Yellow Sea Cold WaterMass communities dominated by cold water species, which changed slightly inspecies composition since the1950s; The mixed communities with the coexistence ofcold water species and warm water species, as had been reported previously; Thepolychaete-dominated eurythermal communities in which the composition changedconsiderably as some dominant species disappeared or decreased. Nine infaunalclusters and five epifaunal clusters were identified in2007. These clusters wereclassified into two groups of communities: The deep water communities whichremained the same as the Yellow Sea Cold Water Mass communities; and the shallow water communities including previous reported mixed communities and eurythermalcommunities, dominated by widely ranged polychaetes.The depth, temperature and median grain size were identified as the majorenvironmental variables influencing the faunal patterns in1992. Species distributionswere related to the depth, temperature and salinity in2007. The subset of depth andtemperature showed the maximum correlation with the biotic matrix.