Species composition and diversity of pelagic Decapods in the East China Sea

Based on the data of four seasonal oceanographic censuses in the East China Sea(23°30′～33°N、118°30′～128°E)in 1997～2000,the species composition and the diversity of pelagic Decapods as well as their relations with environmental variables were discussed.The results showed that there were totally 9 different species,and 7 were in spring and summer respectively,4 in autumn and only 5 in winter.Lucifer intermedius,L.hanseni,L.typus,L.penicillifer and Leptochela gracilis were common species of pelagic Decapods in the East China Sea.The others were rare species.According to the calculated alternation fraction(R),the species composition showed a clear seasonal alternation with the changes of seasons from spring to summer、summer to autumn and autumn to winter.Except the common species,the five rare species were alternately in different seasons.Moreover,the environmental variables have different impacts on the distribution of pelagic Decapods species numbers in different seasons.The distribution in winter and spring were related with the water temperature.However,the salinity was a major determinant of the distribution in summer and autumn.The causal analysis of relation between distribution of species number and seasonal change showed that the distribution of species number in winter and spring depended on ebb and flow of the Taiwan Warm Current and the Yellow Cool Waters.The distribution in summer was related with change of the Changjiang Diluted Water and warm current.Because some common species of pelagic Decapods,such as L.intermedius,could adapt at different environment,these species usually showed high occurrence and very large values in their abundances.This would cause the uneven distribution of different species in the East China Sea,which was the major reason to the low diversity of pelagic Decapods in the East China Sea.