LONG-TERM FIELD ACTOGRAPHY TO ASSESS THE TIMING OF FORAGING EXCURSIONS IN THE LIMPET PATELLA-VULGATA L

Continuous automatic recording was carried out of foraging activity of Patella vulgata from two shores in North Wales, one of which is expos ed to greater wale action than the other. The aim was to undertake a v ery detailed analysis of the temporal organisation of foraging activit y of limpets throughout the spring-neap cycle. The timing was consiste ntly similar at the two sites, in a combined tidal-diel pattern. Most of the limpets showed greatest activity peaks at time of nocturnal low tide, but a few animals on each shore moved during high tide. When, t hrough tidal progression, a nocturnal low tide changed to daytime phas ing, limpets showed a great reduction of activity, after which activit y shifted to the time of the next low tide. This occurred at the times of spring tides. The long term time budgeting of the limpets on the t wo shores was also assessed by considering the fraction of time spent away from home during the entire study period. In this comparison limp ets from one shore exposed to greater wave action spent a longer time away from the home scar than the more sheltered shore limpets, possibl y due to the lower food availability in the exposed shore. Temporal pa tterning of foraging activity shown by P. vulgata is discussed in term s of possible circatidal and circadian rhythmicity regulated by exogen ous environmental factors, and compared with timing of other intertida l molluscs. The observed behavioural polymorphism (inter-individual va riability in the temporal pattern) is sought as a possible mechanism r educing the temporal predictability of, and therefore the vulnerabilit y of mobile limpets to predators.