Fig. 1From: Habitat-specific size structure variations in periwinkle populations (Littorina littorea) caused by biotic factorsStudy areas in the south-eastern part of the North Sea. Investigations and field experiments were performed on mixed beds of blue mussels Mytilus edulis and oysters Crassostrea gigas in the north of the island of Sylt and on the rocky shore of the island of Helgoland (marked by black arrows)Back to article page