Enchytraeus albidus was fed with Fucus, green algae, Zostera marina and Delesseria. Judging from absorption of food, rate of reproduction and duration of life, the animals preferred the plants in the sequence given above.As the putrefaction of a Fucus substrate advances, more and more enchytraeids leave it. A changing salinity of the substrate also influences the number of emigrating worms, increasing it from 15-45‰, but decreasing it towards 60‰. Fed with Fucus E. albidus tolerates a salinity of 60-70‰ on sand for more than 4 weeks, on filter paper only 50‰ for about one week.Reproduction is possible at salinities up to 40‰. Cocoon production is most frequent at 5‰. The mortality of young worms within the cocoons is lowest at 15‰. The incubation period is significantly shorter at salinities of 0-15‰ than at 30 and 40‰.As a terrestrial immigrant to the seashore Enchytraeus albidus secondarily enlarged its range of poikilosmosis, tolerating a concentration of 72‰ in its coelomic fluid for some time. At low salinities it maintains a remarkable degree of hyperosmosis.