Dietary preferences of the common periwinkle, Littorinalittorea (L.)

Abstract

In gustatory choice experiments with mature macroalgae, grazing by the common periwinkle, Littorina littorea (L.), was highly selective in favour of the foliose ephemeral green algae, Ulva lactuca L. and Enteromorpha intestinalis (L.) Link. The fucoid, Ascophyllum nodosum (L.) Le Jol., and the calcareous red alga, Corallina officinalis L., were rejected even under conditions of considerable nutritional duress. Results of attractiveness trials were similar, emphasizing the important selective rôle of gustatory considerations. Macroalgal edibility was not influenced by a prolonged period of starvation or by enforced habituation to a non-preferred species. There was, however, some evidence to suggest that previous feeding experience altered algal attractiveness significantly, prompting less discriminate feeding. A high degree of selectivity was also apparent for algal germlings. Lawns of germling Ulva lactuca and Enteromorpha intestinalis were strongly preferred to juvenile Mastocarpus stellatus (Stackh.) Guiry (= Gigartina stellata (Stackh.) Batt.), Fucus serratus L. and especially Ascophyllum nodosum. Consistent preferences were displayed for adult over juvenile Ulva lactuca and for juvenile rather than adult Fucus serratus. Experimental examination Littorina littorea microdistribution on the mid-and lower shore reveals that, at sheltered sites, individuals forage predominantly on the rock surface and amongst the understorey of ephemeral algae. Higher up the shore and at exposed sites cast-up “drift” seaweeds assume an important dietary rôle. In controlled population experiments on the shore, Ascophyllum nodosum was not grazed. Consequently, this species cannot be considered a potential food source for Littorina littorea, even on those regions of the shore where it may constitute the only macroalgal cover.