Feeding habits of newly hatched juveniles of an intertidal predatory gastropod, Nucella emarginata (Deshayes)

The feeding habits of juvenile Nucella emarginata ( = Thais emarginata), a marine prosobranch gastropod with direct development, were examined to determine when predatory feeding begins, and if ontogenetic shifts in mode of feeding occur. Most hatchlings did not attack live prey during the first 3 days after emerging from their egg capsule. By day 10, however, over 80% of the hatchlings had attacked prey. The late onset of predatory feeding appears to be ontogenetic, rather than a consequence of handling or experimental conditions. Hatchlings did not use alternate food types (mussel feces, algae, biofilm, or barnacle moults), as determined indirectly by growth, survival and organic content measurements of hatchlings. Once N. emarginata started attacking prey, six species of invertebrates which co-occur with the hatchlings in the field were consumed: three bivalves ( Lasaea spp., Musculus taylori and Mytilus spp.) and three barnacles ( Balanus glandula, Chthamalus dalli and Pollicipes polymerus). Hatchlings did not attack limpets ( Lottia pelta and Lottia digitalis), a littorine ( Littorina scutulata), the bivalve Hiatella arctica, or other hatchlings. In addition, hatchlings were able to survive for up to 120 days without food. Although no ontogenetic shift in mode of feeding was observed in young N. emarginata, at least two prey species consumed by hatchlings cease to be used during ontogeny. Possible reasons for the late onset of feeding are discussed.