Littorina mariae — a factor structuring low shore communities?

Abstract

The role of littorinids in structuring communities is discussed. On hard substrates preferential grazing of the dominant algae often enables competitively inferior species to utilize the rock substrate. Investigations of these systems has led to the proposal of a number of factors that should be analyzed in order to assess the effect of herbivores on community structure. Some of these factors have been investigated for Littorina mariae Sacchi & Rastelli. L. mariae is a micro-epiphytic grazer browsing the surface covering of epiphytes off the alga Fucus serratus (L.). The relationship between the host alga, F. serratus, and L. mariae is far more intricate than that between winkles and hard substrates as the alga itself is a dynamic resource. L. mariae is spatially and temporally linked to F. serratus. L. mariae is found almost exclusively on the alga and is positively attracted by extracts of the alga. The life history of the winkle is closely synchronized with that of the alga (the winter decrease of L. mariae populations is associated with the seasonal die-back of the host alga). On analysis of the factors considered important to assess herbivory, and examples of the effects of other epiphytic herbivores on algal success, it is suggested that L. mariae could potentially play an important role in structuring the community of it’s host fucoid and that this may influence larger scale community structure. Experimental manipulations are proposed to evaluate these hypotheses.