Idotea chelipes can tolerate wide salinity variations, but is limited by preference for shelter of branched algae. Jaera normanni is more euryhaline than J. albifrons and is restricted to more variable habitats by competition with the latter. Gammarus duebeni is most euryhaline, and is normally restricted to a very variable environment by competition with other species at each limit of its range, being able to extend into fresh water at Scarlett Point where G. pulex is absent. Procerodes ulvae seems to be limited mainly by physical factors.