Food dependent movement of periwinkles (Littorina littorea) associated with feeding fronts

Consumer aggregations have the potential to drastically change the distribution and availability of resources. One form of aggregation observed in marine benthic invertebrates is the feeding front: a dense band of consumers that travels in a directional manner through a food patch, leaving a cleared area behind it. By artificially creating spatial heterogeneity in the distribution of a filamentous green alga, the formation of a feeding front of periwinkles Littorina littorea was induced on a rocky intertidal shore. The position of the front, the density of snails that comprised it, and the movement of individual snails in and around the front were monitored over a period of 14 days. During that period, the front advanced at an average speed of 2.25 cm d-1 and the density of snails in the front varied between 10 and 24 snails 100 cm-2. Temporal variation in snail density was negatively correlated with wave action. Snails on the trailing edge of the front or on bare rock behind the front exhibited directional movement towards the front, but snails in the front moved shorter distances than those on bare rock. These results support previous findings of resource-dependent movement as a causal mechanism of front formation in marine benthic habitats.