Evaluation of Redox-Mediated Responses of Coral Symbiotic Dinoflagellates to Nano-Selenium

This study investigated species-specific physiological and redox responses of two coral symbiotic dinoflagellates, Cladocopium sp. and Durusdinium sp., to green-synthesized nano-selenium (SeNP) gradients, with implications for eco-friendly marine antifouling. Growth, photosynthetic pigments, antioxidant enzymes (SOD, POD, CAT), lipid peroxidation (MDA), and osmo-protectants were assessed to elucidate mechanisms. Both species exhibited a biphasic (hormetic) response, with stimulation at low concentrations and inhibition at high levels. At 50–100 mg L−1, Cladocopium sp. showed enhanced growth, pigments, antioxidant activity, and osmotic regulation, with reduced oxidative stress, indicating improved redox homeostasis. In contrast, ≥150 mg L−1 disrupted redox balance and suppressed growth. Durusdinium sp. displayed slower growth but maintained stable pigments, consistent antioxidant activity, and low MDA, reflecting a tolerance-oriented strategy. Overall, SeNPs synergistically regulate antioxidant systems and osmotic homeostasis to balance the intracellular redox status of symbiotic dinoflagellates, indicating their potential as antioxidant agents to improve the growth performance of symbiotic dinoflagellates in coral nursery cultivation.