Vulnerability of settling plaice Pleuronectes platessa to predation:: effects of developmental stage and alternative prey

Plaice Pleuronectes platessa L. metamorphose when they change from a pelagic to a benthic habitat during settlement. The effect of developmental stage (i.e. before, during and after metamorphosis) on the vulnerability of reared plaice was tested in laboratory experiments with the epibenthic brown shrimp Crangon crangon as predator. The developmental effect was studied in the presence and absence of the alternative prey Corophium volutator to investigate if the predator's preference for plaice would change with developmental stage. In addition, I investigated the size dependency of shrimp predation on metamorphosing plaice. The vulnerability to predation decreased from the last bilaterally symmetrical stage to the early juvenile stage of plaice, with metamorphosing plaice being intermediate in vulnerability. The decrease was primarily caused by a developmental change in the ability to evade the predator following an encounter. Presence of alternative prey decreased mortality in all developmental stages of plaice, but no interaction was found between the effect of developmental stage and alternative prey to indicate a change in prey preference by the predator. The rapid change in vulnerability to predation during metamorphosis suggests that the developmental stage at settlement is of great importance for the initial survival of plaice recruits. Predation by shrimps on metamorphosing plaice was inversely size-dependent and related to the predator's ability to hold on to the prey once captured.