The antiviral agent, amantadine, is widely present in marine ecosystems and poses a significant threat to marine organisms. However, studies on the toxicity of amantadine across the full life cycle of the brown alga Laminaria japonica, particularly during the microscopic gametophyte stage, remain lacking. A comprehensive approach combing biochemical analyses and multi-omics techniques was employed to investigate the mechanisms underlying amantadine-induced toxicity in L. japonica gametophytes. The development rate of algal cells was less than 3 % from 10