Antioxidant Defense of Mytilus galloprovincialis Mussels Induced by Marine Heatwaves in Correlation with Marteilia Pathogen Presence

Background: The effects of climate change negatively affect marine bivalves' health. Lately, the intensity of marine heatwaves poses serious threats to the aquatic environment setting of high-risk bivalve farming. Since temperature increases can jeopardize bivalves' immunity response, pathogen infection becomes more evident. Reactive oxygen species (ROS) production, increased during the process of phagocytosis, is confronted by the animals' antioxidant defense system. However, apart from pathogenic infections, antioxidant defense responses are also induced by seawater temperature increases; Methods: To enlighten the antioxidant status of Mytilus galloprovincialis originating from mortality events enhanced by intense heatwaves in Thermaikos Gulf, northern Greece, along with Marteilia refringens infection, we examined the expression of genes related to antioxidant defense (catalase, CuSOD and mt10) along with the lipid peroxidation levels and activity levels of antioxidant enzymes (catalase, SOD and glutathione reductase); Results: Our results exhibited increased levels of all these biomarkers. This increase was intensified in the Marteilia infected individuals; Conclusions: Our findings shed light on the oxidative and antioxidant status of farmed mussels led to mortality in the context of Marteilia infection. The latter is augmented by the synergistic effect of heatwaves causing a significant increase in oxidative damage and subsequent antioxidant defense.