Complementary chemical and effect-based risk assessments reveal ecotoxicological risks in Caribbean coastal bays and coral reefs

Anthropogenic chemical pollution poses a significant, yet often unquantified threat to coral reef ecosystems. This study investigated the occurrence, dispersal, and ecotoxicological risks of chemical mixtures in three inland bays of Curacao (Southern Caribbean) and adjacent coral reefs during wet and dry seasons. Passive sampler extracts were analyzed with targeted chemical analysis and effect-based methods. Inland bays acted as reservoirs for chemical pollution, each exhibiting a unique chemical fingerprint likely linked to surrounding land use. Targeted chemical concentrations were higher during the wet season, particularly inside the bays, indicating rainfall-driven mobilization of terrestrial contaminants. Many compounds exceeded their predicted no-effect concentrations, while mixture toxic pressure was low to moderate and highest inside the bays. In contrast, bioassays integrating the effects of the entire mixture revealed a potential ecotoxicological risk, with activation of the Nrf2 oxidative stress pathway dominating across reef sites. The two lines of evidence were complementary: target compounds identify the bays as pollution sources, while bioassays show mixture effects are strongest on the reefs. Hence,targeted chemical analysis alone is insufficient to evaluate ecotoxicological risk. Our multidisciplinary approach provides a framework for prioritizing key chemical indicators and bioassays to monitor coral reef water quality.