Study on abundance variation of pteropods in the East China Sea

On the basis of the census in four seasons from 1997 to 2000 in the East China Sea (23°30′￣33°N, 118°30′￣128°E), the horizontal distribution of pteropods, the seasonal variations of their abundance and dynamic mechanisms of these variations were approached with quantitative and qualitative methods. Results showed that the total abundance of pteropods varied clearly with the seasons in an order of decrease of autumn (108×10-2 ind./m3), summer (33×10-2 ind./m3), winter(28×10-2 ind./m3) and spring (10×10-2 ind./m3). Pteropods were not observed in the north nearshore of the East China Sea (29°30′￣33°N, 122°30′￣125°E)in winter and spring. In all seasons, the peteropod abundance was higher in the south than that in the north and higher in the offshore than that in the nearshore. The major species influencing the peteropod abundance were Creseis acicula in spring, Creseis virgula in summer, Desmopterus papilio in autumn and Limacina trochiformis in winter. The variation of pteropod abundance showed a prominent linear correlation with the surface water temperature and 10 m water temperature, but no significant correlation with both the bottom water temperature and salinity. In summer, the high-abundance distribution area of pteropods was located in the place where the Taiwan Warm Current branchedfromtheKuroshio. Inautumn, thedistributionareawithanabundancehigherthan250×10-2ind./m3expanded northward along with the Taiwan Warm Current within the mixing area where the Changjiang freshwater, the Fujian—Zhejiang coastal water and the Huanghai Sea Cold Water met together. Water temperature and warm currents were the most important environmental factors that influenced the changes of pteropod abundance in the East China Sea.