Abstract

Based on the data from four oceanographic censuses in the East China Sea （23°30′－33°00′ N, 118°30′－128°00′ E）during 1997－2000, and by means of qualitative and quantitative parameters, we analyzed the species composition, species number, and species diversity of pteropods and their relationships with environmental factors. A total of 21 pteropods species were observed in the East China Sea, of which Creseis acicula， Limacina trochiformis，Agadina syimpsoni， Desmopterus papilio，C. virgula var. comica， Cavolinia longirostris，Creseis virgula，C. clava，Hyalocyliz striata and Paraclione longicaudata were common species; Limacina inflata and Pneumoderma atlanticum were subordinate species; and the remaining 9 species were rare. According to seasonal alteration rates (R), obvious alternations of pteropods species occurred from spring to summer and from autumn to winter. The species number of pteropods peaked in autumn (20 species), followed by summer (15 species) and winter (14 species), and was lowest in spring (5 species). Results of regression analysis showed that the distribution of species number was affected only by water temperature in spring and winter, whereas it was dependent on water temperature, 10-m salinity and bottom salinity in summer and autumn. In winter and spring, because of low temperature and a nearshore weak warm current, species number was relatively low, and species diversity (H′) was greater in the south or in nearshore areas than in the north or nearshore. From summer to autumn, though this trend still remained, the difference between nearshore and offshore areas was significantly reduced. This is because the Taiwan Warm Current brought more species to the nearshore region and the north part of the East China Sea.