ABSTRACT

The effects of sunscreen onscleractiniancorals have garnered widespread attention; however, the toxic effectsand mechanisms remain unclear. This study investigated the toxicological effects of two common inorganicfilters used in sunscreens,nanozinc oxide and titanium dioxide (nZnOandnTiO₂), on the reef-building coralGalaxeafascicularis, focusing on the phenotypic, physiological, and transcriptomic responses. The results showedthat after exposure to 0.8 mg/L ofnZnOand 30 mg/L ofnTiO₂ for 48 h, all coral polyps exhibited retraction. ZnandTiions were detected in coral tissues at concentrations of 67.18 and 24.87μg/g, respectively, indicating theaccumulation ofnZnOand nTiO₂in coral tissues. The zooxanthellae density,Fv/Fm, and chlorophyll-a contentdecreased significantly. The activity of antioxidant enzymes showed an increasing trend. Meanwhile, glutaminesynthetase and glutamate dehydrogenase activities exhibited a decreasing trend. The health status of corals wasimpacted as a result ofnZnOandnTiO₂ stress. Transcriptomic analysis showed that the toxicity mechanisms ofnZnOand nTiO2 differed in corals. Following exposure tonZnO, differentially expressed genes (DEGs) in coralswere mainly enriched in signaling pathways related to immune response. The genes related to innate immunity,such as MASP1, MUC5AC, TLRs, and C2, were significantly upregulated, indicating thatnZnOexposure inducesan innate immune response in corals. Meanwhile, followingnTiO₂ exposure, the upregulated DEGs were mainlyenriched in signaling pathways related to transporter activity. In contrast, the downregulated DEGs were mainlyenriched in energy metabolism pathways, indicating thatnTiO₂ disrupted the energy supply of corals, therebyleading to an increased demand for nutrient transport. This study reveals the toxic effects ofnZnOandnTiO₂, andtheir mechanisms of action onscleractiniancorals, providing a reference for further assessing the toxicity ofsunscreen on corals.