Seasonal and spatial distribution of chaetognaths on the north-west continental shelf of the South China Sea

Abstract

The seasonal variation and spatial distribution of chaetognaths were studied based on samples collected from July to August 2006 (summer), December 2006 to January 2007 (winter), and in April 2007 (spring) on the north-west continental shelf of the South China Sea. A total of 19 species of chaetognaths were identified. The average chaetognath abundances (mean ±SD) were 54.0 ± 44.5, 36.8 ±16.7 and 48.9 ± 95.5 ind. m−3 in summer, winter and spring, respectively. Flaccisagitta enflata and Serratosagitta pacifica were the dominant species during the whole sampling period, and F. enflata determined the spatial distribution of total chaetognath abundance. According to the topography and hydrological conditions, the survey area was divided into three sub-regions: inshore waters of the western Guangdong (Region I), inshore waters to the east of Hainan Island (Region II) and offshore waters from the western Guangdong to Hainan Island (Region III). The community structure and abundance distribution of chaetognaths varied significantly between the three sub-regions. The species richness was significantly different among the three sub-regions, with the lowest in Region I and the highest in Region III. The species richness was correlated positively with temperature and salinity. The abundance of chaetognaths was significantly higher in Region I than in both Regions II and III in summer and spring. The increasing food availability caused by the cold eddy, coastal upwelling and the western Guangdong coastal current was able support a greater abundance of chaetognaths during warm seasons on the north-west continental shelf of the South China Sea.