Brackish-water submergence of the common periwinkle, Littorina littorea, and its digenean parasites in the Baltic Sea and in the Kattegat

Abstract

North Sea and Baltic Sea populations of Littorina littorea differ with respect to their vertical distribution. In the North Sea L. littorea is strictly intertidal while in the Baltic Sea maximum population densities occur in the sublittoral. Levels of infestation with larval digenetic trematodes diminish qualitatively (number of species recorded) and quantitatively (number of hosts infested) with decreasing salinity. Both the host and two parasite species -Cryptocotyle lingua and Microphallus pygmaeus - display 'brackish-water submergence' under conditions of reduced surface salinity. © 1984 Biologische Anstalt Helgoland.