The Preliminary Study Of Community Structure Of Nekton In The Subtropical Seas Of China

The data of this study are from the survey of swimming animals in September 2017(summer),November 2017(Autumn),March 2018(winter)and may 2018(spring).By studying the species composition,ecological type,dominant species and important species,community structure,diversity index and community stability of swimming animals in Xinghua Bay,we can understand the general situation of the community and resources of swimming animals in the sea area,so as to provide basic research for further understanding the resource situation of swimming animals in subtropical sea area,as well as provide theoretical basis for the construction,utilization and restoration of the project in Xinghua Bay.A total of 127 species of nekton were identified in the four seasons,belonging to 21orders and 64 families 98 genera,including 51species in spring,79 species in summer,37 species in autumn and 50 species in winter.Analysis by category,a total of 79 kinds of fish,43 kinds of crustaceans,5 kinds of cephalopods.According to the classification and analysis,the species of Perciformes is the most abundant accounting for 37 species;followed Flatfishes,Clupeiformes,Scorpaeniformes,each of eight kinds;then 4 kinds of Anguilliformes.According to the analysis of biomass composition,fish accounted for59.95%,crustaceans accounted for 38.09%,and cephalopods accounted for1.96%.According to the number composition analysis,fish accounted for 17.84%,crustaceans accounted for 81.78%r;cephalopods accounted for 0.37%.Most of the fish in Xinghua Bay are shallow water fishes,and there are many estuarine fishes,which are related to the geographical location of the sea and hydrological factors.The species composition and seasonal distribution of fish are mainly affected by fish migration.Due to the overfishing of Engraulidae in the East China Sea,the trend of decline also exists in this area.Crustaceans are mostly economic and common species in the East China Sea.In addition,the mouth of Xinghua Bay is the spawning ground and bait ground for nekton.The IRI of the dominant species of Pagrus major in the whole was 5122.There are five species of important species in the whole year,which are Atypopenaeus stenodactylus,Parapenaeopsis hardwickii,oratosquillina interrupta,Pagrus major and Solenocera crassicornis.The IRI values are 405,267,263,261,105.The IRI of the dominant species in spring was 5122.In summer,there are two dominant species,Leptochela gracilis and Atypopenaeus stenodactylus,the IRI is 6085and 1955 respectively.In autumn,there are two dominant species,Leptochela gracilis and Harpadon nehereus,the IRI is 3450 and 1277 respectively.The IRI of the dominant species of Leptochela gracilis in winter was 2906.The dominant species and important species in Xinghua Bay are mostly local species or migratory species.The seasonal change of dominant species is related to fish migration and shrimp reproduction.The dominant species of shrimp decline from medium-sized to small-sized.The ecological types of fish are divided according to temperature and habitat water layer.From the perspective of temperature adaptability,the number of warm-water species>warm-temperature species>cold-temperature species,warm-water 46 species,warm-temperature 31 species,and 2 species of cold-temperature.From the perspective of the inhabit water layer,there are 56 species of bottom fishes,12 species of near-bottom fishes,and 11 species of middle-pelagic fishes.Crustaceans are divided into three major ecological groups:wide temperature and low salt,wide temperature and wide salt,and high temperature and high salt according to the research of Song Haitang,Yu Cungen and others.The wide temperature and low salt water system formed by the coastal waters of Xinghua Bay,the external high temperature and high salt water system,and the wide temperature and wide salt water system formed by mixing the two,determine the ecological characteristics of nekton in Xinghua Bay.The results of non-metric multidimensional scaling analysis(MDS)show that the four seasons plots have a certain explanatory significance.Cluster analysis(CLUSTER)analysis shows that spring can be divided into three groups at the level of 25%similarity,summer can be divided into three groups at the 30%similarity level,and autumn can be divided into 15%similarity levels.Winter can be divided into two groups at the level of16%similarity.ANOSIM analysis shows significant differences between the four season groups.The community characteristics in spring and autumn related to species richness and hydrological conditions of the station.The structure of nekton communities is greatly affected by seawater salinity in summer.In winter,the structure of nekton communities related to channels.The Shannon?Wiener diversity index(H?)from 0.93 to 2.13,the highest in summer and the lowest in autumn;Pielou's evenness index(J?)from 0.50 to 0.71,the highest in summer and the lowest in autumn;the Margalef?species richness index(D)from 1.81 to3.50,the highest in summer and the lowest in autumn.The average biomass resource density of nekton is 113.51 kg/km~2,the highest is station 12(212.83 kg/km~2),the lowest is station 3(29.24 kg/km~2),the average tail resource density is 84.82×10~3 ind./km~2,the highest is station 4(520.27×10~3 ind./km~2),and the lowest is station 7(13.51×10~3ind./km~2).The seasonal turnover index(AI)of the four seasons is above 96,and the migration index(MI)in summer and winter is close to 0,which indicates that the migration of species of nekton in Xinghua Bay is in a non dynamic equilibrium state.The results of ABC curve show that the community of nekton in Xinghua Bay is seriously disturbed except in winter.The intensity of the disturbance of is as follows:Winter<spring<autumn<summer.The strong disturbance in summer is caused by typhoons.