EFFECTS OF EXPERIENCE AND RISK OF PREDATION ON THE FORAGING BEHAVIOR OF THE SOUTH-EASTERN PACIFIC MURICID CONCHOLEPAS-CONCHOLEPAS (MOLLUSCA, GASTROPODA)

1. Different size classes of the muricid Concholepas concholepas (Brug uiere)(small and medium subadult specimens inhabiting mainly the high- and mid-intertidal, and large adult ones inhabiting mainly the subtida l) were assessed for handling times and diet selection by offering the m three different sizes of the high-intertidal mussel Perumytilus purp uratus (Lamarck). 2. The effect of experience on the foraging efficien cy of the different size classes of the muricid was tested by comparin g the handling times of specimens starved after collection from the fi eld with those of specimens subjected to starvation after having been exclusively fed with this mussel. 3. Experienced predators showed a co nsistent reduction in handling time with corresponding increase in pre y profitability, although this varied in magnitude in the nine distinc t predator/prey size combinations. As a consequence, foraging experien ce changed the profitability ranking of different classes of prey.4. P rey-size preferences changed with foraging experience in accordance wi th the associated variations in prey profitabilities. Particularly, th e number of attacks per unit time and the average weight of the mussel s consumed by the different size classes of C. concholepas increased w ith experience, while the total time devoted to foraging decreased sli ghtly. 5. The exposure of experienced C. concholepas to effluent from a higher-order predator, the subtidal asteroid Meyenaster gelatinosus (Meyen), induced the muricid to reduce the time devoted to foraging. T his reduction in foraging time was achieved differently, according to the size of the forager: small individuals reverted to their initial p reference for smaller mussels, while medium and large individuals redu ced the number of attacks. Both effects lowered the rate of food intak e, which must be seen as a cost of reducing risk of predation.