Fig. 3From: Habitat-specific size structure variations in periwinkle populations (Littorina littorea) caused by biotic factorsMean abundance (±SD) of different size classes of Littorina littorea in the mid intertidal, low intertidal and shallow subtidal zone on mussel beds of the sedimentary shore at Sylt (a), and on the rocky shore at Helgoland (b). At each tidal level, six replicate samples (n = 6) were taken. Zeros indicate complete lack of periwinklesBack to article page