Growth inhibition of native Littorina saxatilis (Olivi) by introduced L. littorea (L.)

Abstract

Since its introduction to North America, Littorina littorea (L.) has become the most abundant periwinkle on New England shores. The possible effect of this introduction on the native populations of L. saxatilis (Olivi) was investigated by setting up mixed and single species cages at three tidal heights in two habitats at Woods Hole, Massachusetts. L. saxatilis is most abundant in the upper intertidal and black lichen zones, while L. littorea is most abundant in the mid and low tidal zones. Both species grew significantly more at lower than at higher tidal levels. Food scarcity appears to set an upper limit to the vertical distribution of L. littorea. At the low tidal level the presence of L. littorea depressed the growth rate of L. saxatilis, while L. littorea grew better in the presence of L. saxatilis than conspecifics. Food competition may be the mechanism of this interaction.