CulturesA. tonsa culture was supplied by the National Institute of AquaticResources, Danish Technical University, Denmark. The copepodcultures were cultivated at two different salinity seawaters: theoriginal salinity of 32‰ and an additional low salinity of 10‰. Thelow salinity culture was obtained by gradually diluting half of theoriginal culture with deionized water over a period of two weeks.Copepod cultures were fed three times per week with a unialgaldiet of Rhodomonas salina cultured in 32‰-salinity f/2-medium(Guillard and Ryther, 1962). A culture of the epibiotic euglenoidC. vesiculosum was provided by CCAP (Culture Collection of Algaeand Protozoa, Scottish Marine Institute, UK; strain number 1211/3).C. vesiculosum, originally grown in freshwater Jaworski’s Medium(CCAP), was gradually acclimatized to a mixture of 10‰-salinityf/2 and Jaworski’s Medium, reaching a final salinity of 5‰. All cul-tures were maintained at 15◦C under dim light following a 12:12 hlight/dark photoperiod.