Abstract

The scallop Argopecten purpuratus is a valuable marine resource in coastal regions where climate change is intensifying upwelling events, potentially imposing physiological stress that compromises immune function. Hemocytes, the primary immune cells in scallops, may be particularly vulnerable to these stressors. This study evaluated hemocyte stress status and immune competence in scallops maintained for one year in suspended culture systems under naturally varying upwelling intensities, and in scallops exposed for 17 days to controlled conditions simulating intense and non-upwelling scenarios. Cellular stress was assessed via expression of antioxidant enzyme genes (ApSOD, ApCAT, ApPrxV), the stress protein HSP70, and oxidative damage (MDA levels). Immune function was evaluated under baseline and post-infection conditions (with Vibrio crassostreae in the laboratory), through analysis of hemocyte count, infiltration, viability, and antibacterial activity. Compared to moderate or weak upwelling in the field, and non-upwelling conditions in the laboratory, intense upwelling resulted in: (i) upregulation of stress-associated genes in the field and following infection in the laboratory; (ii) increased oxidative damage after bacterial challenge; (iii) reduced circulating and infiltrating hemocytes; (iv) elevated hemocyte mortality; and (v) decreased antibacterial activity. These findings suggest that intense upwelling induces oxidative stress and impairs hemocyte-mediated immune responses in A. purpuratus, potentially increasing susceptibility to pathogens. This study enhances our understanding of how climate change-driven upwelling affects scallop physiology and immune defense, with important implications for aquaculture sustainability and disease management.