Route selection in the foraging of Patella vulgata (Mollusca : Gastropoda)

The prosobranch limpet Patella vulgata is an intertidal grazer performing l ooped excursions centred on a home scar. Foraging within each excursion is mostly concentrated around the point of maximum distance from home. The ori entation of the foraging excursions in a group of limpets was analysed on a vertical substrate on a sheltered shore in North Wales. The spatial relati onship between different excursions of the same individual was also analyse d. A total of 174 complete excursions from 47 adult limpets were obtained u sing the LED (light emitting diode) tracking technique. In particular, the leaving direction and the direction of the main foraging area of each excur sion were computed. When considering the foraging strategy over five consec utive days, a substantially radial cropping pattern was evident at both the population and individual level, with no evident directional preference. H owever, when considering consecutive excursions of the same individual a co ncordance in leaving directions was evident in about 40% of cases. The high overlap between the outward branch of the trajectory of one night and the homing branch of the previous one suggests that the directional decision ca n be based on a trail-following mechanism. Moreover, our data suggest that directional decisions are taken at the beginning of each excursion when lea ving home.