Direct and indirect effects of Littorina littorea (L.) on barnacles growing on mussel beds in the Wadden Sea

摘要: On the extensive sedimentary tidal flats of Wadden Sea, beds blue mussel Mytilus edulis represent only major hard substratum and attachment surface for sessile organisms. this substratum, barnacle Semibalanus balanoides is most frequent epibiont. In summer 1998, it occurred on over 90% large mussels (>45 mm shell length) dry weight barnacles reached 65% weight. However, extent overgrowth not constant differs widely between years. Periwinkles (Littorina littorea) may reach densities >2000 m−2 intertidal beds. Field experiments were conducted to test effect periwinkle grazing densities. An experimental reduction bulldozing pressure by periwinkles resulted in increased recruitment barnacles, while numbers decreased with increasing snail density. The highest survived absence L. littorea. a lack activity also facilitated settlement ephemeral algae which settled later year. showed that growth rate presence these algae. Thus, littorea reduce initial settlement, but indirectly increase reducing It suggested density be key factor population dynamics S. Sea.