TIME PARTITIONING OF FORAGING IN THE LIMPET PATELLA-VULGATA

(1) The behavioural ecology of the limpet, Patella vulgata L., a common grazing intertidal mollusc, was investigated at Lough Hyne in south-west Ireland. Foraging in limpets has previously been shown to be a simple three-phase system: an outward travelling phase, a middle phase of intense foraging, and a period of return travel to the permanent home scar. (2) A predictive model was developed and considered the following strategies as the controlling factors for limpet foraging: (i) while foraging, limpets maximize their net energy gain; (ii) while foraging, limpets minimize their energy costs; (iii) while foraging, limpets minimize the time spent away from the home scar. Data were collected from the field to provide the morphological and behavioural parameters, and from various literature sources for the energetic parameters used in the model. (3) Limpets do not appear to forage so as to maximize their net energy gain; this is probably due to the predictability of foraging periods for limpets. The strategy of cost minimization also provided poor estimates for the time budgets observed; probably this is because the animals require energy for growth of the somatic and gonadal tissues. The partitioning of time between travelling and intense foraging by a limpet while foraging can, however, be explained in terms of strategy (iii), that of time minimization. (4) The possible environmental constraints which could influence limpet foraging trips and how these change with increasing height up the shore are discussed. The possibility that the 'feeding' trips may, in addition, maintain the algal biofilm in a highly productive phase is also discussed. The foraging behaviour of limpets varies between different sites around the British Isles, and it is suggested that this may be due to varying combinations of predation and desiccation risks.