Determining optimal temperature and salinity for marine organisms is a challenge for marine ecologists because not every species can be easily maintained in the laboratory for testing the influence of environmental parameters. To find a simple method to estimate the optimal temperature and salinity for marine organisms based on survey data, a reciprocal quadratic yield-density model was used for determining the optimal temperature or salinity from abundance data for six pelagic Chaetognatha species. The data for the modelling were collected in four surveys in the East China Sea (23°30′–33°N 118°30′–128°E) from 1997 to 2000. According to both survey data and results from the models, we analysed qualitatively and quantitatively the ecological characteristics of those species. Estimated optimal temperatures and salinities are 17.3°C and 14.1‰ for Sagitta nagae, 20.3°C and 13.8‰ for S. bedoti, 24.9°C and 32.9‰ for S. enflata, 22.5°C and 16.5‰ for S. ferox, 24.5°C and 34.1‰ for S. pacifica and 17.3°C and 14.1‰ for S. pulchra, respectively. Three ecological groups were evident in the East China Sea: the neritic, warm temperate water species (S. nagae); the neritic, warm water species (S. pulchra, S. ferox and S. bedoti); and the oceanic, warm water species (S. enflata and S. pacifica). Our results validate that the model is applicable for describing the relationship between chaetognaths abundance and temperature or salinity.
