Community Structure Of Fish Eggs And Larvae Of The Zhejiang Of Central And Southern Coastal Waters In Spring And Autumn

Based on the survey data of horizontal trawl resources in the range of27°00′-29°30′N and 121°00′-123°00′E(0–80m isobath)in the coastal waters of Zhejiang Province from 2020 to 2021,this paper quantitatively analyzes the spatial distribution pattern,species diversity characteristics and environmental impact of fish eggs and larvae in the coastal waters of Zhejiang Province from various angles by using different analytical methods(sweep area method,relative importance index method,diversity index method,Wald method,canonical correspondence analysis method and spatial analysis method).From the perspectives of time and space,the uncertainty of spatial pattern of fish eggs and larvae,the variability of temporal pattern and the difference in the influence of environmental factors on them in the coastal waters of Zhejiang Province were discussed.The quantitative distribution and spatial distribution characteristics of fish eggs and larvae in Zhejiang coastal waters were analyzed.A total of 5999 eggs and 1610 larvae were collected.The total species number of fish eggs and larvae was 80,belonging to 10 orders and 38 families.According to the density distribution of fish eggs and larvae in spring and autumn of 2020 and 2021,the density distribution of fish eggs and larvae is relatively high in the adjacent waters of Dongtou Islands and at the junction of Oujiang Estuary and Yueqing Bay.According to the ecological characteristics,fish eggs and larvae of Zhejiang coastal waters were divided into three types: estuary species,coastal species and offshore species.During the years,the number of offshore species were the largest.According to the temperature-adapted components,fish eggs and larvae were divided into warm water species;warm temperate species;cold temperate species.During the years,fish eggs and larvae are mainly warm water species and warm temperate species,warm temperate species are the largest.Seasonal and interannual differences also exist in the density distribution of inshore fish eggs and larvae and offshore fish eggs and larvae.From the abundance of fish eggs,the average abundance of inshore fish eggs and offshore fish eggs in spring and autumn of 2020 is higher than that in spring and autumn of 2021.The Arc Gis density distribution map shows the seasonal and interannual variation of fish eggs.The number of fish eggs and the frequency of station occurrence in spring 2020 are higher than those in autumn 2020.From the annual comparison,the number of fish eggs and the frequency of station occurrence in spring2020 are higher than those in spring 2021.From 2020 to 2021,the dominant species of fish eggs were Harpodon nehereus and Chrysochir aureus,the dominant species of fish larvae were Stolephorus sp.In spring,the fish eggs and larvae in the coastal waters of Zhejiang Province are mainly clustered in the Dachenyang spawning ground.In autumn,the fish eggs and larvae move outward as a whole,and are clustered in the waters near the forbidden fishing area line.The diversity index was used to analyze the seasonal differences of biological diversity of fish eggs and larvae of Zhejiang coastal water areas.The richness index,diversity index and evenness index in April2021 were the highest,and the early resources of fish of Zhejiang coastal waters area were in a moderate disturbance state.Based on the cluster analysis of Wald method in Spss and CCA canonical correspondence analysis in Canoco,We analysed the spatial distribution pattern of fish eggs and larvae.the relationship between dominant species,divergent species and water depth,surface temperature and surface salinity were obtained either.In the spring of 2020,the main species causing the difference of fish eggs between the inshore stations and offshore stations were the Harpodon nehereus,mainly gathered in the offshore stations,and had a significant positive correlation with Depth,SSS and SST.In the spring of 2021,the main species causing the difference in fish egg species between the inshore stations and offshore stations was Larimichthys polyactis,which was mainly concentrated in the inshore stations,and was negatively correlated with SST.In the autumn of 2020 and 2021,the main species that caused the differences in fish egg between the inshore stations and offshore stations were Harpodon nehereus and Chrysochir aureus,which were mainly clustered in the offshore stations,and showed significant negative correlation with Depth,SST and SSS.In the spring of2020,the main species causing the difference of fish larvae between the inshore stations and offshore stations were Liza haematocheilus and Amblychaeturichthys hexanema,which were mainly clustered in the inshore stations and negatively correlated with SST.In the autumn of 2020,the main species of fish larvae causing the difference between the inshore stations and offshore stations were Harpodon nehereus,mainly clustered in the offshore stations,and positively correlated with Depth,SST and SSS.In the spring of 2021,the main species that caused the difference of the larvae between the inshore stations and offshore stations were Liza haematocheilus,mainly gathered in the inshore stations,which was positively correlated with SST.In the autumn of 2021,the main species that caused the differences of larvae between the inshore stations and offshore stations were Stolephorus sp.and Larimichthys croceus,which were mainly clustered in the inshore stations.According to the sea surface temperature,sea surface salinity and water depth,the coastal waters of Zhejiang Province are divided into two different waters: offshore waters and inshore waters.The inshore waters of Zhejiang are mainly distributed in the coastal estuaries and coastal areas of central and southern Zhejiang Province.The water depth is 0～40 m,showing the characteristics of low temperature and low salinity.Different seasons has different distribution areas.The main species are coastal estuarine species(Liza haematocheilus,Lateolabrax japonicas,Acanthogobius ommaturus,Amblychaeturichthys hexanema etc.).The offshore waters were mainly distributed in the outer edge of central and southern Zhejiang with the water depth of 40–80 m,showing the characteristics of high temperature and high salinity.The sea area is mainly distributed in the sea area west of the forbidded fishing area line.The main species composition is offshore species(Trichiurus lepturus,Scomber japonicas,Psenopsis anomala,etc.).The above research results showed that the spatial pattern of fish egg and larvae community structure and its influence on marine physical environment,and the changes of water depth,surface temperature and surface salinity affect the species composition and diversity of fish eggs and larvae community structure in Zhejiang coastal waters.This study reveals the interaction between early biological resources of fish species,fish eggs and other organisms and non-biological environment,plays a significant role in the structure and function of marine ecosystems,especially the stability of marine ecosystems.Zhejiang coastal waters is one of the largest fish spawning grounds in the East China Sea.It is closely related to the early life history of fish,spawning period and nursery,which will provide scientific basis for the formulation of conservation strategies,fishery management and ecosystem restoration of new spawning grounds and nursery.