Species Composition And Distribution Of Fish Larvae And Juveniles In The Western South China Sea During Summer And Autumn

The larval and juvenile fish were taken as the research object in the western South China Sea in this study.15 sampling stations were set in the area of 110°E～115°E and10°N～16°N during summer and autumn of 2012.WP2 Plankton nets（mouth diameter,57 cm;mesh size,200μm）were used vertically from 200m depth to the sea surface at a speed of 1ms^-1.The obtained data were used by SPSS,PRIMER and CANOCO software to analyze density,relative importance index,species diversity index,cluster analysis and canonical correspondence correlation.The species composition and species diversity characteristics of the larval and juvenile community in the western South China Sea during summer and autumn were discussed.The correlation between larval and juvenile fish and environmental factors was also discussed.The purpose of this investigation is aimed to provide a scientific basis for the early complementary mechanism,population changes,and fishery management of fish larvae and juveniles in this area.A total of 784 fish larvae and juveniles were collected in this survey,belonging to98 species in 38 families.Among them,660 individuals belonging to 78 species were collected in summer.One hundred and twenty-four individuals belonging to 41 species were collected in autumn.In summer,the dominant species were Vinciguerria sp.（39.70%）,Stephanolepis cirrhifer（11.21%）,Caranx sp.（5.45）.%)and Benthosema pterotum（1.97%）.In autumn,the dominant species were Gobiidae sp.（15.32%）,Ceratoscopelus townsendi（7.26%）,Diaphus sp.（6.45%）,Astronesthes sp.（5.65%）and Callionymidae sp.（4.03%）.The Margalef Richness Index（D）and the Shannon-Wiener diversity index（H’）revealed the same seasonal variation which the value was higher in summer than in autumn.However,the Pielou’s index of evenness（J’）in autumn was higher than that in summer.Similarity cluster analysis results indicated that larval fish assemblages in summer can be divided into two communities:larval fish in the cyclonic eddy and larval fish in the anticyclonic eddies.While in autumn,the larval fish assemblages can be divided into three communities:larval fish without influence of the cyclonic eddy,larval fish influenced slightly by the cyclonic eddy and larval fish gathered near the center of the cyclonic eddy.According to the MDS ranking test,the stress indexes are less than0.2,indicating that the sorting effect has certain credibility.The variations of abundance and assemblage of larval fish might be attributed to sea surface temperature（SST）,sea surface salinity（SSS）and sea level anomaly（SLA）.