Microbiome Dysbiosis and Decreased Survival in Coral Larvae Exposed to Environmentally Relevant Concentrations of Nanoplastics and Sulfamethoxazole

Scleractinian corals are increasingly threatened by environmental contaminants such as nanoplastics (NPs) and antibiotics. The early life stages of corals are particularly vulnerable to environmental stressors, yet their impacts under environmentally relevant concentrations remain poorly understood. Here, we exposed Pocillopora damicornis larvae to NPs (100   μg/L) and sulfamethoxazole (SMX, 0.1   μg/L) for 48   hours to assess their effects on survival, settlement, tissue structure, and bacterial symbionts. Exposure of NPs and SMX significantly reduced larval survival, caused tissue necrosis and mesenterial filament dissociation, and altered the composition of bacterial symbionts, including an decrease in Pseudoalteromonas . Compared to the Control group, co-exposure of NPs and SMX induced more severe tissue damage and broader functional shifts in microbial communities, including elevated methylotrophy, photoheterotrophy, photoautotrophy, and reduced anaerobic respiration. These findings suggest that coral larvae are highly sensitive to NPs and SMX, which may alter bacterial symbiont community to disturb nutrient cycling and energy metabolism, cause tissue damage, and ultimately impair larval survival, thereby threatening coral reef replenishment and recovery.