A Study On The Structural Characteristics Of Ichthyoplankton In The Middle Of Zhejiang Province Coastal Waters

Based on the survey data of April 2017,November and April 2018,November,this article carried out four voyages surveys of fish eggs and larvae in the middle of Zhejiang Province coastal waters.Using relative importance index(IRI),non-metr ic multi-dimensional scaling,cluster analysis and canonical correspondence analysis(CCA)and other methods,the species composition,dominant species,community str ucture characteristics,spatial distribution of species density and its relationship with environmental factors in this sea area were comprehensively analysed.The following were the research results of this article:(1)During the spring and autumn of 2017-2018,a total of 2924 fish eggs and 2092 fish larvae of 66 species were collected from 4 voyages.They belonged to 27 families and 9orders.In spring and autumn of 2017,46 species of fish eggs and larvae were collected from 2 voyages,belonging to 19 families and 7 orders;In spring and autumn of 2018,50 species of fish eggs and larvae were collected from 2 voyages,belonging to 24 families and9 orders.The species and numbers in spring in two years were more than in autumn,and the interannual changes of the dominant groups were not obvious.In April 2017,the dominant species of fish eggs was Liza haematocheilus,and the dominant species of fish larvae was Chaeturichthys stigmatias;in November,the dominant species of fish eggs and fish larvae were both Harpodon nehereus.In April 2018,the dominant species of fish eggs were Liza haematocheilus and Eupleurogrammus muticus,the dominant species of fish larvae was Chaeturichthys stigmatias,and the dominant species of fish eggs in November was Harpodon nehereus.The species alternative rate in spring and autumn in 2017 and 2018 was relatively high,both above 90%.(2)The analysis of the species diversity index showed that the richness index(D),diversity index(H')and evenness index(J')were higher in spring than in autumn in the two years,all indexes in autumn 2017 were lower than in other seasons.Cluster analysis and NMDS sorting graph showed that the stations in spring,autumn of 2017 and autumn of2018 were divided into four groups,while the stations in spring 2018 were divided into three groups.The results of SIMPER analysis showed that the characteristic species withinthe group and the divergent species between the groups was little difference,and the species with the highest contribution rate of similarity and dissimilarity in each group were mainly the bottom fish such as Liza haematocheilus,Harpodon nehereus and Chaeturichthys stigmatias.The environmental factor analysis showed that the abundance of fish eggs was significantly correlated with salinity,depth and temperature,the fish eggs and larvae were greatly affected by temperature and salinity.(3)This study found that there were fish eggs and larvae of economic fish such as Larimichthys croceus,Larimichthys polyactis,Trichiurus lepturus and Eupleurogrammus muticus were extremely low in the middle of Zhejiang Province coastal waters,indicating that the sea area is still a spawning and breeding ground for economic fish,compared with the situation of fishery resources before 1970 s,at present,the dominant species in this area are mainly small demersal fishes,which indicates that the status of fishery resources in this sea has greater changes.Therefore,the restoration of the ecological environment of the sea area and the scientific management of fisheries should be strengthened to achieve the healthy and sustainable development of fish resources in the sea area.