Deciphering mechanisms of UV filter- and temperature-induced bleaching in the coral Acropora tenuis, using ecotoxicogenomics

Abstract

Coral reefs are at risk of bleaching due to various environmental and anthropogenic stressors such as global warming and chemical pollutants. However, there is little understanding of stressor-specific mechanisms that cause coral bleaching. Therefore, conducting accurate ecotoxicological risk assessments and deciphering modes of action of potentially deleterious ultraviolet (UV) filters (sunscreen compounds) are crucial issues. In this study, we evaluated the toxicity and bleaching effect of benzophenone-3 (BP-3), which is widely used in sunscreen products, on the reef-building coral Acropora tenuis. Furthermore, to understand differences in UV filter- and temperature-induced bleaching, a comparative ecotoxicogenomic approach using RNA-seq was integrated into a toxicity test to clarify differences in gene expression changes induced by BP-3 and heat stress (31{degrees}C). The lethal concentration 50% (LC50) was calculated as 3.9 mg/L, indicating that emission level of BP-3 was properly controlled based on the risk assessment. Differentially expressed genes related to oxidative stress and extracellular matrix organization were involved in coral responses to both BP-3 and heat stress, but their patterns differed. Whereas immune and heat-shock responses were activated in response to heat stress, activation of a drug metabolism pathway and several signal transduction pathways were identified in BP-3 treatment groups. Our study enhances understanding of stress responses in corals induced by UV filters and thermal stress. Using potential gene markers identified in this study for eco-epidemiological surveys of stressed corals, we urgently need to develop effective countermeasures.