Ocean acidification affects predator avoidance behaviour but not prey detection in the early ontogeny of a keystone species

In a series of laboratory Y-maze experiments, we investigated the directional res - ponse of juveniles of the muricid snail Concholepas concholepas, a rocky-shore keystone predator characteristic of the southeastern Pacific coast, in displaying prey detection and predator escape behaviour after 5 mo rearing under contrasting levels of pCO²: 390 (present-day), 700 and 1000 μatm CO² (as expected in near-future scenarios of ocean acidification [OA]). Regardless of the experimental condition, juveniles significantly chose the Y-maze arm containing prey. In general terms, the directions of the displacement paths of the snails in the Y-maze were straight from the starting point to the final position, where the prey items were offered. Moreover, juveniles reared at present-day concentrations and 700 μatm CO² significantly avoided displacement in the Y-maze arm receiving predator odours. This predator-avoidance behaviour was disrupted in juveniles reared at 1000 μatm CO². In most cases, displacements recorded under such conditions were sinuous, and the trial individuals did not significantly choose the predator-free arm. In contrast, displacement paths recorded for snails reared at present-day concentrations and at 700 μatm CO² were straight from the initial to the final position, with displacements mostly ending near the prey and in the arm free of cues associated with predation. The loss of responses to a natural predator under high pCO ² levels in the early ontogeny of C. concholepas may result in ecologically deleterious decisions by this keystone species. We conclude that the negative effects of OA on the chemosensory behaviour of keystone species could have negative consequences for community dynamics.