Predation on barnacles of intertidal and subtidal mussel beds in the Wadden Sea
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Balanids are the numerically dominant epibionts on mussel beds in the Wadden Sea. Near the island of Sylt (German Bight, North Sea), Semibalanusbalanoides dominated intertidally and Balanuscrenatus subtidally. Field experiments were conducted to test the effects of predation on the density of barnacle recruits. Subtidally, predator exclusion resulted in significantly increased abundances of B. crenatus, while predator exclusion had no significant effects on the density of S. balanoides intertidally. It is suggested that recruitment of B. crenatus to subtidal mussel beds is strongly affected by adult shore crabs (Carcinus maenas) and juvenile starfish (Asterias rubens), whereas recruits of S. balanoides in the intertidal zone are mainly influenced by grazing and bulldozing of the very abundant periwinkle Littorina littorea, which is rare subtidally. Thus, not only do the barnacle species differ between intertidal and subtidal mussel beds, but the biotic control factors do so as well.