Study on ecology of chaetognaths in Pearl River Estuary

Based on the data obtained from 12 cruises from 2002 to 2003 in the Pearl River Estuary,the species composition and abundance variation of chaetognaths were reported and environmental influence on chaetognaths were discussed.The Pearl River Estuary can be divided into three regions according to the surface salinity,region Ⅰ(salinity25),region Ⅱ(salinity from 25 to 30) and region Ⅲ(salinity30).The results showed that total 13 species occurred in the Pearl River Estuary,most of which were belonged to the warm-water species.The species richness was higher in regions Ⅱ and Ⅲ than in region Ⅰ.The results from three large cruises(Jul.2002,Jan.and Apr.2003) showed that the average abundance of chaetognaths in the Pearl River Estuary was 23 ind/m3.The average abundances were 43,15 and 11 ind/m3 in region Ⅱ,Ⅲ and Ⅰ,respectively,and it was higher in spring and summer than in winter.Another result from 9 small cruises in region Ⅰ only showed that chaetognath abundance generally was increased from the inner to outer of the estuary.Sagitta bedoti and S.enflata were the dominant species in the Pearl River Estuary.Salinity,temperature and food concentration play an important role in abundance variation of chaetognaths in the Pearl River Estuary.