Thermo-haline tolerance of Ciona intestinalis (L., 1767) at different developmental stages.

The tolerance of a population of C. intestinalis from the Venetian Lagoon to various combinations of temperature and salinity has been tested at different stages of its biological cycle. Mortality rate, growth and a "life quality index" have been evaluated. Young animals mainly differ from adults in the interaction between temperature and salinity: this is of high-high type in the former and of high-low type in the latter. Young animals are more resistant than adults to low temperatures; this fact could explain the presence of the species in coastal environments with winter temperatures under 10°C. Developing eggs are less tolerant to temperature and exhibit a high-low thermo-haline interaction, as it is for adults. The optimality centres at the different stages lie at a salinity of about 35‰ and at a temperature between 15 and 20°C. We can conclude that our population does not present any noticeable adaptation to the lagoon environment; on the contrary it is well adapted to the average conditions of the Mediterranean Sea. Our results are finally compared with those obtained by other Authors on different populations of the same species.