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 exposed to greater wale action than the other. The aim was to undertake a very detailed analysis of the temporal organisation of foraging activity of limpets throughout the spring-neap cycle. The timing was consistently 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, through tidal progression, a nocturnal low tide changed to daytime phasing, limpets showed a great reduction of activity, after which activity 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 two shores was also assessed by considering the fraction of time spent away from home during the entire study period. In this comparison limpets from one shore exposed to greater wave action spent a longer time away from the home scar than the more sheltered shore limpets, possibly due to the lower food availability in the exposed shore. Temporal patterning of foraging activity shown by P. vulgata is discussed in terms of possible circatidal and circadian rhythmicity regulated by exogenous environmental factors, and compared with timing of other intertidal molluscs. The observed behavioural polymorphism (inter-individual variability in the temporal pattern) is sought as a possible mechanism reducing the temporal predictability of, and therefore the vulnerability of mobile limpets to predators.