From mucus barrier disruption to cellular damage: Multiscale toxic effects of Benzophenone-3 on a reef-building coral

Coral reefs are increasingly exposed to emerging contaminants such as benzophenone-3 (BP-3), a UV filter widely detected in coastal environments. This study provides an integrative, multiscale assessment of BP-3 toxicity in the reef-building coral Seriatopora caliendrum, combining physiological, cellular, biochemical, and tissue-level responses. Corals were exposed for 96-h to relevant concentrations of BP-3 (0.3, 1.3, 2.5, 5, and 10 mg/L), and bleaching, pigment loss, zooxanthellae density, chlorophyll a content, oxidative damage, lysosomal stability, and mucocyte composition were quantified. The 96-h EC₅₀ for bleaching was 3.999 mg/L, indicating that the coral exhibited relatively low sensitivity to BP-3. Bleaching intensity increased with concentration and was characterized by elevated RGB values, and a marked reduction in zooxanthellae. Cellular biomarkers indicated oxidative stress, evidenced by a significant increase in carbonylated proteins and lysosomal membrane instability detected by the neutral red retention assay, however no statistically significant differences were observed for DNA damage and TBARS. Histochemical analyses showed a progressive loss of neutral glycoproteins (PAS) indicating compromised mucus integrity. At higher concentrations (5-10 mg/L), extensive tissue loss prevented biochemical and histological assessment. Collectively, the results demonstrate that BP-3 induces multilevel biological disruption, from molecular damage to tissue degradation, highlighting its potential ecological risk to coral reefs, particularly in heavily touristic areas. These findings support the need for environmental monitoring and regulation of UV filters in sensitive marine ecosystems.