Buried and forgotten: Plastic contamination in an ancient deep-sea fish lineage

Microplastics are ubiquitous in the hydrosphere, with the ocean floor widely recognised as their ultimate sink. However, their impacts on deep-sea fauna remain poorly understood, particularly among scavenging species, key players of benthic food webs. Hagfishes (Myxini), an ancient lineage within Craniata (>300 million years), possess a unique morphology: an elongated, scaleless, and finless body, with a cranium but lacking jaws and vertebrae. Adapted to life in soft sediments, they remain buried for extended periods and often aggregate to consume the carcasses of large fishes and cetaceans. In addition to scavenging, they actively prey on benthic invertebrates. Here, we provide the first documented evidence of plastic ingestion in hagfishes, based on a gastrointestinal tract (GIT) analysis of Myxine mcmillanae collected at ∼900 m depth in the Caribbean Sea. Microplastics were identified in all specimens using stereoscopic analysis and pyrolysis-gas chromatography/mass spectrometry, with an average concentration of 4302.3 ± 3785.3 μg GIT^-1 g^-1 and 3.3 ± 2.2 particles per individual (771.1 ± 1034.1 μm). These values exceed those reported for omnivorous and planktivorous fishes from similar depths and are comparable to levels observed in invertebrate scavengers, suggesting trophic transfer via carrion consumption. The dominance of high-density, hazardous polymers, especially polyvinyl chloride (1778.5 ± 1956.3 μg GIT g^-1), raises concerns about potential health implications. Our findings highlight the overlooked vulnerability of deep-sea scavengers to plastic pollution and emphasise the need to incorporate them into broader assessments of microplastic contamination and its ecological consequences across marine food webs.