Abstract The spatial and temporal changes in species composition and abundance of pteropods in relation to hydrography in the waters around Taiwan were investigated during the period from February 2003 to August 2004. In total, 26 species of pteropods belonging to 11 genera and 4 families were identified, with mean abundance of 75.87¡Ó11.39 inds/100m³, The abundance of pteropods exhibited noticeable seasonal changes, higher in summer and lower in winter. Higher abundance were always found in Taiwan Strait in our study area. The six most dominant species were Limacina inflata, Creseis acicula, C. clava, C. virgula, L. bulimoides and C. virgula var. conica in descending order. These species totally accounted for more than 88¢H of the total pteropods. The composition of dominant species were similar among different seasons and hydrographic areas, but the order of dominance was different. Different dominant species showed different seasonal distribution patterns. The species number of pteropods in the waters around Taiwan showed no difference among seasons. There were 21 species found in winter, 22 species in spring and summer. The species number was higher in the waters of eastern Taiwan. The diversity index of pteropods in summer was significantly higher than that in spring and winter. The total abundance, species number, and diversity index of pteropods were significantly positively correlated to water temperature; only the species number was significantly positively correlated to salinity. The abundance of the six most dominant species showed different correlations with water temperature and salinity. The abundance of Creseis clava and C. virgula were significantly positively correlated with water temperature, but Limacina. bulimoides was negatively correlated. The abundance of L. inflata and L. bulimoides displayed significant positive correlation with salinity, but C. clava displayed negative correlation.

This study collected zooplankton and hydrographic data in the Taiwan Strait (TS) using the cruises of ¡§Fishery Research I¡¨ from January 2005 to October 2006, to investigate the seasonal and spatial distribution of planktonic pteropods associated with hydrographic conditions. In total, 29 species of pteropods belonging to 10 genera and 5 families were identified, with mean abundance of 97.14 ¡Ó 66.16 ind./100 m3. The abundances and species number of pteropods exhibited apparent seasonal changes, abundance was higher in summer and lower during winter, while species numbers was higher in fall and lower in winter. Pteropods showed higher diversity in oceanic waters than in shallower shelf waters, but the abundance showed no significant difference. The night-time abundance and species number were significantly higher than the day-time. The effect of typhoon on the abundance and species numbers of pteropods was not significant. The four predominant species found in this study area were Creseis clava, Creseis acicula, Limacina inflate and Limacina trochiformis, together they accounted for 95% of the total pteropod catch, among these, C. clava constitued 48% of the total catch. The pteropod communition was similar among seasons, but ranked differently. Different dominant species showed different seasonal distribution patterns. The distribution of pteropods showed no clear spatial difference in the TS, but higher species richness was usually observed in the southern TS. The pteropods found in this study mostly belonged to the widespread oceanic species, and the dominant species were similar to the previous studies in the South China Sea. The total abundance, species number, and species diversity index of pteropods showed significantly positive correlation with the seawater temperature, and the species number was negative correlated with salinity. Among the four predominant species, the abundance of C. clava, C. acicula, and L. trochiformis were positively correlation with seawater temperature, meanwhile, C. acicula and L. trochiformis showed significantly negative correlations with salinity. This study proposed that the abundance, species number, and species diversity of Pteropods were not obviously influenced by typhoon, instead seasonal succession of water masses and day/night change might be the important factor affecting the distribution patterns of pteropods.