The scallop Argopecten purpuratus is a species of high commercial interest in northern Chile and Peru. Both natural and cultured populations are located in shallow bays which are periodically subjected to decreases in the levels of dissolved oxygen and to variations in the availability of food, due to upwelling events or large-scale oscillations such as El Niño–Southern Oscillation. The aim of the present study was to evaluate how the nutritional status of A. purpuratus juveniles affects their escape capacity (as a measure of their vitality) after exposure to hypoxia cycles such as those encountered in their natural environment. For this, three feeding levels were applied for 15 days: scallops fed with a mixture of microalgae equivalent to (1) 6% or (2) 3% of their body mass and (3) unfed scallops. Subsequently, half of the individuals in each treatment underwent daily hypoxia cycles for 7 days and the other half was maintained under normoxia. After this period, using their predator, the sea star Meyenaster gelatinosus, the scallops were induced to escape, and several escape response indicators were evaluated. In general, scallops fed with the highest microalgal ration (6% of scallop mass) showed the best escape performance in terms of the reaction time to the predator, total number of claps, and clapping time and rate, closely followed by scallops fed 3% of their mass. Unfed scallops showed the poorest performance in each of these escape parameters. These results were closely related with the carbohydrate content of the adductor muscle, with unfed scallops showing the lowest content. Hypoxia exposure resulted in a decrease in escape response, and unfed scallops were the most affected. Among unfed scallops, 40% of the individuals maintained under normoxia showed an escape response, whereas only 15% of those exposed to hypoxia escaped the predator. By contrast, and regardless of environmental oxygenation, more than 90% of individuals fed with either 3% or 6% rations escaped the predator. In conclusion, when scallops are under reduced nutritional state (due to low food availability), the cyclical hypoxic periods that they encounter in the natural environment can have profound effects on their vitality, making them more vulnerable against predators.
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Vol. 38 • No. 2