Combined effects of fluoroquinolone antibiotic enrofloxacin and rising sea temperatures on the health of the Mediterranean mussel (Mytilus galloprovincialis): Exploring physiological, biochemical, and energetic balance dynamics.

Human activity exposes organisms in marine ecosystems to numerous stressors, including rising seawater temperatures and antibiotic contamination. The present study investigated the impacts of environmentally relevant concentrations of the fluoroquinolone (FQ) antibiotic enrofloxacin (ENR), specifically 5 and 500 ng/L, in Mytilus galloprovincialis under ambient (20 °C) and predicted warming (25 °C) conditions after 14 days of exposure, followed by a 14-day recovery period in the absence of ENR. The chemical analyses revealed significant variability in bioaccumulation in mussel tissues. Physiological assessments showed decreased respiration and filtration rates post-exposure, with temperature-dependent recovery dynamics. Biochemical parameters indicated an increased metabolic capacity and energy reserves at higher temperatures, with a significant increase in energy expenditure. Notably, ENR induced significant DNA single-strand breaks in mussel gills and digestive glands, with temperature influencing DNA repair mechanisms. The combination of ENR and elevated temperatures exhibited additive or even synergistic effects on certain physiological and biochemical parameters, indicating a higher risk when these stressors act together. The Indipendent Action model (IA) results highlighted that the majority of observed effects in combined stressors were consistent with predicted values, with notable synergistic interactions in energy reserves and antagonistic responses in metabolic and physiological functions. These findings suggest that both stressors, acting alone and especially in combination, may pose a risk to marine bivalves such as mussels. Further research is needed to assess the impacts of FQs and ocean warming on ecosystem stability and non-target organisms.