Study On Community Structure And Species Diversity Of Fish In Dongtou Outside Sea Area

Based on the bottom trawl survey data from April 2018(spring)and October 2018(autumn)in Dongtou outside sea area,the community structure characteristics and species diversity of fish in the Dongtou outside sea area,as well as the ecological relationship among fish in this area by using the methods of ecological type,resource density,species turnover rate,relative importance index,cluster analysis,ABC curve,species diversity and niche breadth and overlap.And the status of species diversity,as well as the ecological relationship between fish in the sea area.The main results are as follows:In the Dongtou outside sea area,53 species of fish were identified in spring and autumn,belonging to 47 genera,29 families and 10 orders.There were 21 species of fish in the two seasons,and the replacement rate was 60.4%.There are 38 species of fish in spring,belonging to 8 orders,21 families,34 genera,36 species in autumn,belonging to 9 orders,20 families and 31 genera.In spring and autumn,the highest percentage of tail centimeters and biomass was the Harpadon nehereus.The percentage of biomass was 50.56%.The average tail resource density in spring is 8270.3ind/km~2,the average biomass resource density is 63667.5g/km~2,and the average tail resource density in autumn is 8087.4ind/km~2,and the average biomass resource density is 160555.9g/km~2.For the characteristics of fish resource density plane distribution,the resource density of station near the islands in spring and autumn is relatively high,the density of station resources in the coastal waters of spring is much higher than that of the outer sea area,and the difference of resource density between the coastal waters and the outer sea area is not big.The ecological types of fish in this area are mainly warm and warm water-based fish,and spring and autumn are more warm-water fish than warm-temperature fish,accounting for more than 60%of the total number of fish species.In spring,the dominant species are the Harpadon nehereus and the Sardinella zunasi,and the important species are 6.In autumn,the dominant species are the Harpadon nehereus and the Muraenesox cinereus,and the important species are 5.The Harpadon nehereus is the common dominant species in the two seasons.Twenty stations in spring were divided into two groups according to CLUSTER clustering and NMDS ranking.The coefficients of community clustering stress were 0.1.ANOSIM similarity analysis showed that there were significant differences between the two groups of fish communities(R=0.932,P<0.01).Simper was used to analyze the contribution rates of the typical species in each group and the divergent species that caused the differences between groups.The typical species in group A included three species,Harpadon nehereus,Engraulis japonicus and Decapterus maruadsi.The total contribution rate was 91.29%.Typical species in group B included three species,Harpadon nehereus,Chaeturichthys stigmatias and Trypauchen vagina,with a total contribution rate of 90.31%.The differential contribution rate of group A and B was 90.22%,including 11 different species.Twenty stations in autumn were also divided into two groups.The coefficients of community clustering stress were 0.14.ANOSIM similarity analysis showed that there was a significant difference between the two groups(R=0.722,P<0.01).There was a significant difference between the two groups in the contribution rate of typical species and between groups.The typical species in group C included the Harpadon nehereus,the Collichthys lucidus and the Chrysochir aureus.The contribution rate of three species was93.74%,and there was only one typical species(Harpadon nehereus)in group D.The difference between group C and group D was 90.39%,included 9 species.In the spring and autumn,the W values in the ABC curve method are positive and close to 0.In the spring,Dongtou outside sea area fish stations calculate species diversity indices based on their biomass,the Shannon-Wiener Diversity Index H'is between 0.017~1.753,and the average is 0.987;Pielou evenness index J'is 0.025~0.906,the average value is 0.474;Margalef Rich index D is between 0.120~2.166 and the average is 1.105.Autumn Shannon-Wiener Diversity Index H'is between 0.504~1.676,the average value is 1.031;Pielou evenness index J'is 0.229~0.791,the average value is 0.475;Margalef richness index D is 0.587~2.133,the average is 1.066.In spring and autumn,the niche breadth values varied greatly.In spring,the niche breadth values of the faucet fish ranged from 3.16 to 0.02,the highest was 3.16,and the lowest was 0.02.In autumn,the niche breadth values of the faucet fish ranged from 4.41 to0.02,the highest was 4.41,and the lowest was 0.02.The values of niche breadth and relative importance index showed the same trend in the two seasons,that is,the regression analysis showed that the fitting effect of logarithmic equation was the best,that is,R~2 was0.7 in spring and 0.9656 in autumn.In spring,the overlap value of niche was between 0.00and 0.99,the distribution degree was not uniform,the range of variation was very large,in which 47 pairs of species with Oik>0.6 were 47 pairs,accounting for 6.67%of the total species logarithm;The niche overlap value in autumn was between 0.00 and 0.96,the degree of niche overlap was not uniform,in which 46 pairs of species with Oik>0.6were46 pairs,accounting for 7.3%of the total species logarithm.In conclusion,the fish seasonal turnover in the Dongtou outside sea area is high,the dominant species is simplification,the community clustering is obvious,the diversity of species is low,the dominance of low-value fish such as Harpadon nehereus and Sardinella zunasi is obvious,the niche breadth is strong,the stability of community structure is poor,and the overall situation of fish resources is not optimistic.