Diversity Of Fish Larvae And Juveniles In The Water Area Of Chongming Dongtan, Yangtze River Estuary

In this study,larvae and juvenile fish communities in Chongming Dongtan and surrounding waters of Yangtze River Estuary were selected as research objects.Based on the sample data collected in November 2020(autumn),January 2021(winter),April(spring)and August(summer),the species composition and spatial distribution of larvae and juvenile fish were studied.In order to provide important reference for fish habitat restoration and fishery management in the Yangtze Estuary,the relationship between community structure,species diversity and environmental factors of larvae and juvenile fish was further discussed.From November 2020 to August 2021,14 stations will be set up at Chongming Dongtan and the surrounding waters of the Yangtze River Estuary.At each station,surface horizontal trawling nets(diameter 1.3m,mesh 0.5mm)will be carried out quarterly for 10 min with a towing speed of 2kn/h,and the flow value of each net will be recorded with a network port flowmeter.The collected sample was placed in 5%formalin solution for fixation.The water temperature and salinity were measured by the water quality analyzer HADZS-330,and the turbidity was measured by the turbidity meter ET4200,respectively.The concentration of chlorophyll a was measured by spectrophotometry in the laboratory.A total of 4556 larvae and juvenile fish belonging to 8 orders,14 families and 48 species were collected during the investigation.Perciformes had the largest number of species,with 23 species in 5 families.Clupeiformes followed,with 10 species in 3families.Cypriniforms consist of 5 species in 1 family;Osmeriformes consist of 5species in 1 family;Pleuronectiformes consist of 1 family and 2 species.Anguilliformes,Mugiliformes and Tetraodoniformes all belong to 1 family and 1 species.Coilia mystus had the most individuals,accounting for 25.09% of the total individuals,followed by Stolephorus commersonnii(20.12%),Salanx ariakensis,17.11%),Pseudolaubuca sinensis(11.36%)and Rhinogobius giurinus(4.86%),the above five fish accounted for78.54% of the total number of individuals.According to ecological types,there were 21 species of estuarine fish,13 species of Marine fish,6 species of freshwater fish and 2species of migratory fish.In spring,the dominant species were Odontamblyopus lacepedii,Rhinogobius giurinus,Lateolabrax maculatus.The important species were Neosalanx tangkahkeii and Luciogobius sp.In autumn,winter and summer,there was a single dominant species,which were Salanx ariakensis,Neosalanx tangkahkeii and Coilia mystus,respectively.Among them,Neosalanx tangkahkeii was an important species in spring,while in summer,the IRI values of Stolephorus commersonnii and Pseudolaubuca sinensis were close to 500.The average density of larvae and juveniles in autumn was 0.1085 ind./m~3,and the density of larvae and juveniles in southern branch was higher than that in northern branch.The highest density was found in Z6,where the main species were Salanx ariakensis.Z7 has the smallest density.In autumn,the dominant species of Salanx ariakensis were distributed in both southern and northern branches.The average density of larvae and juvenile fish in winter was 0.0015 ind./m~3,and only Z1 and Z14 were collected.In spring,the average density of larvae and juveniles was 0.1ind./m~3,and the density of larvae and juveniles was the highest at Z7,which was mainly Rhinogobius giurinus.Z17 has the smallest density at 0.0027 ind./m~3.Neosalanx tangkahkeii appeared in both winter and spring,and was the dominant species and the important species respectively.In spring,the densities of the dominant species of Odontamblyopus lacepedii and Rhinogobius giurinus in the northern branch were higher than those in the southern branch.The average density of larvae and juveniles in summer was0.6583 ind./m~3.Z7 is the site with the highest density,mainly was Stolephorus commersonnii.The highest density of the dominant species Coilia mystus appeared in Z5,with distribution in both northern and southern branches.An important species Stolephorus commersonnii is only found in the northern branch station.Pseudolaubuca sinensis only distributed in the southern branch station,and the maximum density appeared in Z3.In spring and summer,the density of larvae and juveniles in the north branch was higher than that in the south branch,and both were concentrated in the outer part of the estuary region.The species richness index(D),diversity index(H’)and evenness index(J’)showed the same trend between seasons,which were the highest in spring and the lowest in winter.The clustering analysis results of autumn showed that all the stations could be divided into three groups: the freshwater group dominated by Neosalanx tangkahkeii;Estuarine groups mainly with Salanx ariakensis;Marine group dominated by Larimichthys crocea.In spring,larvae and juveniles can be divided into fresh water groups mainly composed of Neosalanx jordani;The estuarine group I mainly consisted of Lateolabrax maculatus.The estuarine group II is mainly composed of Rhinogobius giurinus and Odontamblyopus lacepedii.In summer,the larvae and juveniles can be divided into: the estuarine groups mainly composed of Coilia mystus and Pseudolaubuca sinensis;Marine group consisting mainly of Stolephorus commersonnii and Engraulis japonicus.There were obvious differences between larvae and juveniles groups in Chongming Dongtan,but the estuarine groups which could adapt to a wide range of salinity were dominant.The typical correlation results in autumn showed that salinity(SSS)and chlorophyll a(CHL)were the main environmental factors affecting the horizontal distribution of larvae and juvenile fish in the Chongming Dongtan and the surrounding waters of the Yangtze Estuary.Spring was salinity(SSS),turbidity(TUR),summer was salinity(SSS).Pearson correlation matrix analysis showed that salinity(SSS)was the main environmental factors affecting larvae and juvenile fish richness index(D)in spring,while chlorophyll(CHL)and salinity(SSS)were the main environmental factors affecting richness index(D)in summer.Summer diversity index(H’)and evenness index(J’)were correlated with salinity(SSS).