Toxic metals and perfluorobutane sulfonate acid (PFBS) suppress aerobic metabolic capacity and alter hypoxia sensitivity in the marine ostracod Stigmatocythere costa.

Coastal ecosystems face increasing contamination from both legacy trace metals and emerging pollutants such as per- and polyfluoroalkyl substances (PFAS). While ostracods are established environmental indicators, their physiological responses to pollutants, particularly for marine species, remain poorly characterized. We investigated the acute toxicity and metabolic impacts of copper, zinc, and perfluorobutane sulfonate (PFBS) on the marine ostracod Stigmatocythere costa from Hong Kong coastal waters. Ostracods were exposed to concentration gradients of each pollutant for 14 days (mortality) and 7 days (metabolic assays). Survival, routine metabolic rates (MO2), and critical partial pressure of oxygen (Pcrit) were measured using closed respirometry. All pollutants caused concentration-dependent mortality. Copper (25-700 μg L-1) and PFBS (35-600 mg L-1) exhibited toxicity plateaus at lower concentrations before sharp mortality increases, suggesting threshold-dependent cellular damage, whereas zinc (1500-6500 μg L-1) showed a monotonic dose response. Lethal concentration for 50% mortality (LC50) values decreased over time for all three contaminants, indicating increasing toxicity with prolonged exposure. While routine MO2 remained unchanged, exposure to copper (50-100 μg L-1) and PFBS (75 mg L-1) significantly reduced peak MO2, indicating impaired aerobic capacity. Unexpectedly, zinc (2500-4000 μg L-1) and PFBS (75-150 mg L-1) decreased Pcrit, suggesting altered hypoxia sensitivity, potentially reflecting compensatory physiological responses. These findings demonstrate that environmentally relevant concentrations of copper and zinc, comparable to levels in heavily polluted Hong Kong sediments, can constrain aerobic scope in ostracods while altering fundamental hypoxia sensitivity, thereby limiting their capacity to cope with additional environmental stressors and potentially disrupting benthic food web dynamics.