The amphipod Orchestoidea tuberculata, is the numerically dominant scavenger in the upper intertidal levels of sandy beaches from south central Chile. The main food source for juveniles and adults of this amphipod are the macroalgae stranded on the beach. Experiments of food preferences were carried out to analyze the eventual partition on the most common macroalgae on that beaches (Durvillaea antaretica, Macrocystis pyrifera y Lessonia nigrescens) by juveniles and adults of this amphipod. While juveniles preferred to consume L. nigrescens, adults showed a significant preference for D. antarctica. Similar to the laboratory results, that of field studies shows that juveniles of O. tubercula to did not show significant preferences between D. antarctica and M. pyrifera, while adults preferred to consume D. antarctica instead of M. pyrifera. That suggest that D. antarctica is an important source of food (and habitat), for adult amphipods. Due to the fact that L. nigrescens could not be included in the field experiments, the possibility that juveniles also prefer this macroalgae in those conditions remains as an open question. Although the reasons underlying the differences in the food preferences of juveniles and adults are unknown, two possibilities can be proposed: ontogenetic changes in the morphology of mouth structures used for feeding and/or ontogenetic changes in nutritional requirements. However, the fact that juveniles preferred to consume the macroalgae with the lowest nutritional content (L. nigrescens) among the three species offered as food, suggest another explanation to the observed differences. This refers to the. fact, that by preferring different food items, juveniles can avoid the cannibalism of adults, biological interaction previously demonstrated for O. tuberculata.