Species Composition And Spatial Distribution Of Fish Larvae And Juveniles In The Northern South China Sea

This study is based on the data collected from 23 stations set up in the northern South China Sea during summertime of 2012.The larval and juvenile fish samples were collected by the vertical trawl survey with WP2 plankton net(net diameter 57 cm,net length 271 cm,mesh 200μm).The species composition and quantity distribution of fish larvae and juveniles were studied,and the association between them and environmental factors was investigated,and the correlation between the hydrological characteristics of the northern South China Sea and the distribution and assembleges of fish larvae and juveniles was analyzed.The results of this study are as follows:(1)A total of 230 fish larvae and juveniles were collected,comprised of 11 orders,33 families,and 77 species.Of these,46 taxa were identified to the species level.The most diverse order was Perciformes,with 24 species in 16 family,accounting for31.17% of the species of larvae and juveniles in the surveyed sea area.Followed by Myctophiformes and Stomiiformes,18 species in 1 families and 12 species in 4 families,respectively.(2)The changes in the number of fish larvae and juveniles among the stations in the surveyed sea area are more consistent with the change trend of the Margalef index.There were obvious changes in the richness index(D)and diversity index(H’)of larvae and juveniles among the stations in the surveyed sea area,but there was little difference in the evenness index(J’)among stations except for station B7.In general,the fish larval and juvenile fish community structure in the surveyed sea area is relatively stable,and the spatial distribution of diversity has changed significantly.The results of the cluster analysis showed that,according to the geographical location and topography,it can be divided into 2 groups — group I(oceanic group)and group II(offshore group).At the same time,the canonical correlation analysis(CCA)results also show that the temporal and spatial distribution of fish larvae and juveniles in the northern South China Sea is closely related to surface sea temperature(SST)and chlorophyll a(Chl a)concentration.(3)Three peaks of the abundance was found,in eastern Hainan Island,where the coastal upwelling occurred:the diluted water from the Pearl River,and coastal water of the Paracel Islands,where the chlorophyll a concentration was relatively high.However,human activities have affected the ecological environment.Therefore,it is necessary to further enhance the ability of fishery administration and law enforcement,strengthen the monitoring and protection of the ecological environment of the sea area,and ensure the sustainable development of fishery resources in the South China Sea.