Preliminary report on the distribution of chaetognaths in the southern part of the South China Sea

Abstract

This paper reports the distribution of chaetognaths in the southern part of the South China Sea, based on the plankton samples collected by the research vessel CHANGI from April 1970 to April 1972. The chaetognath specimens collected in April, 1972 were identified. Altogether 22 species belonging to 5 genera were discerned. Sagitta enflata was the dominant species and was widely distributed in the areas surveyed. While the common species in the neritic waters are S. bedfordii, S. bedoti, and S. Oceania, the common species in the oceanic province are Krohnitta pacifica, K. subtilis, Pterosagitta draco, S. bipunctata, S. hexaptera, S. lyra, S. minima, S. pacifica and S. regularis. S. enflata and S. ferox are common in both neritic and oceanic provinces. The individual numbers of chaetognaths varies from 400 to 13,000 per 100 m3 of water. In general, the chaetognaths are abundant in coastal waters but decline towards the open sea. Based on the occurrence of the various species, the importance of chaetognaths as biological indicators of water masses are discussed. P. draco, S. hexaptera, S. minima and S. pacifica are useful indicators of the presence of oceanic water in the neritic province. The presence of these species in some neritic waters adjacent to the oceanic province suggests the mixing of oceanic water and neritic water in the respective areas during the survey.