Quantitative Distribution Of Shrimps And Crabs Around The Nanji Islands And Its Relations To The Environmental Factors

The shrimps and crabs data based on comprehensive fishery resources surveys in November,2013 and in February,May,and September,2014 in the Nanji islands area,and studied the species composition,quantitative distribution,dominant species trends and the relation of environmental factions of shrimps and crabs in the Nanji islands area according to the four seasons' survey data and used catch rates as the quantitative index of shrimps and crabs resources distribution.The results are as follows:(1)A total of 48 species were identified which were consisted of 25 species of shrimps and 23 species of crabs.and the shrimps belonged to 17 genera in 9 families,the crabs belonged to 4 genera in 8 families.The number of species in different seasons respectively were autumn(30 species)> spring(29 species)> winter(27 species)>summer(24 species).There were 12 common species in four seasons.Through the analysis of the Index of Relative Importance(IRI)showed that there had only one dominant species-Portunus trituberculatus in one year around,There were 3 species were dominant species in winter which Parapenaeopsis tenella?Charybdis japonica and Portunus trituberculatus.The average biomass and average abundance were highest in summer.The community structure mainly k choice of species which community system has stronger anti-jamming capability in the Nanji islands area.(2)The value of Shannon-Weaver index(H')was highest in winter,spring took second place,and it was lowest in Summer.The value of Margalef index(D)varies greatly,and the value in spring was absolute higher than other seasons.and it was lowest in Summer.The value of Pielou index(J')was closely in four seasons;it was highest in spring and autumn and lowest in summer.(3)The CLUSTER analysis showed that spring,summer and autumn had 3 different community groups,autumn had 2 different community groups.ANOSIM analysis showed that there had obvious difference seasons.SIMPER analysis showed that the average similarity in different group of every season was low.The average dissimilarity of shrimps and crabs group was highest between spring and summer,and it is lowest between winter and spring.(4)The shrimps and crabs biomass and abundance is significant correlation with environmental factors,such as depth,bottom temerature and bottom salinity,it has a big strong infect with biomass and abundance in autumn and winter.but the biomass and abundance in spring and summer is not significant correlation with environmental factors.Shrimp and crabs biomass and abundance distribution changes with the depth of the water distribution is obvious.The diversity index for shrimps and crabs is not significant correlation with environmental factors,it is mainly due to the characteristic in Nanji islands area is complex and changeable salinity,temperature and diverse fauna.