Microplastic Ingestion in Three Deep-Sea Fish Species: First Ecological Insights from Stable Isotope Analysis

Microplastic (MP) pollution is an emerging environmental stressor in marine ecosystems, yet its relationship with trophic ecology remains poorly understood in deep-sea environments. This study investigated MP ingestion in relation to trophic ecology in three deep-sea fish species (Chlorophthalmus agassizi, Hoplostethus mediterraneus, and Coelorinchus caelorhincus) from the central Tyrrhenian Sea (Western Mediterranean). Stable isotope analysis (δ13C and δ15N) was combined with detailed characterisation of ingested MPs to assess trophic niches, trophic position, and species-specific ingestion patterns. The three species showed distinct isotopic signatures, with C. agassizi occupying a lower trophic position, while H. mediterraneus and C. caelorhincus overlapped at higher trophic levels. MPs were detected in all species, with an overall frequency of occurrence of 34.4%, and no significant interspecific differences in occurrence or abundance were observed. However, significant differences emerged in MP characteristics. C. caelorhincus, which exhibited the widest isotopic niche, ingested larger and more diverse particles, whereas C. agassizi showed lower occurrence but higher particle loads in affected individuals. These results suggest that trophic ecology is not clearly associated with MP ingestion rates but may influence the size and diversity of ingested particles, highlighting ecological drivers of exposure in deep-sea ecosystems.