Yield-density model for determining optimal temperature and salinity for zooplankton: case studies with Appendicularia in the East China Sea

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 four Appendicularia species. The data for the modeling were collected in four surveys in the East China Sea (23°30′∼33°N, 118°30′∼128°E) from 1997 to 2000. Our results indicate that the proposed model is suitable for describing the relationship between appendicularian abundance and temperature or salinity. Estimated optimal temperatures and salinities are 27.9 °C and 33.6 for Oikopleura intermedia Lohmann, 1896, 25.2 °C and 33.6 for Oikopleura longicauda (Vogt, 1854), 22.5 °C and 35.0 for Oikopleura rufescens Fol, 1872, and 23.9 °C and 33.8 for Oikopleura dioica Fol, 1872, respectively. The data indicate that O. dioica and O. longicauda are euryoecic species which are able to tolerate a range of temperatures (> 15 °C) and of salinities (> 10), whereas O. rufescens and O. intermedia are stenoecic species with a narrow tolerance range of temperatures and salinities. The distributions of these four species in the East China Sea were highly temperature and salinity dependent.