Microplastic Ingestion by Marine Fish from the Central Tyrrhenian Sea: Toward the Identification of Regional Bioindicators

Microplastics (MPs, synthetic particles <5 mm) are pervasive contaminants that can be ingested by a wide range of marine organisms, entering the trophic web and potentially transporting harmful substances such as additives and adsorbed pollutants. In response to this issue, the Marine Strategy Framework Directive (MSFD) requires EU Member States to establish coordinated monitoring programs. However, the ecological variability among European seas – from the Black Sea to the Baltic, makes the identification of region-specific bioindicators essential. Unlike conventional contaminants, MPs exhibit diverse chemical and physical characteristics. Their environmental behavior and bioavailability depend not only on these properties but also on the ecological traits of the species within a given ecosystem. This study investigated MP ingestion in eight fish species from the central Tyrrhenian Sea. Specimens were collected by professional fishing vessels operating on the continental shelf off the coast of Anzio, approximately 50 km south of Roma. The aim was to assess interspecific differences in both the quantity and type of ingested particles, and to explore how habitat use may influence MP distribution in marine food webs. The ultimate goal was to inform the selection of effective regional bioindicators. Results revealed species-specific variation in ingestion rates, with no significant differences linked to habitat. However, statistically significant differences emerged in the types of MPs ingested across habitats. Pelagic species were more exposed to low-density polymer fragments and films – such as polyethylene, polypropylene, and polystyrene, commonly used in packaging and consumer products. In contrast, benthic-associated species ingested a higher proportion of fibers and filaments from synthetic textiles (e.g., polyester, acrylic), along with denser particles typically linked to fishing gear and industrial sources. Notably, species with the highest ingestion rates were generalist feeders, likely due to their broader prey spectrum and foraging behavior. Conversely, top trophic-level predators ingested a more diverse array of MP particles, suggesting that MPs can be transferred through trophic interactions. These findings indicate that suitable bioindicator species should simultaneously exhibit high ingestion rates and a broad range of ingested MP types. These insights are essential for the development of targeted monitoring strategies. To ensure robust assessments of both MP exposure and the diversity of particles available in marine ecosystems, monitoring programs should include species representing both pelagic and benthopelagic/demersal habitats. Within each, a combination of apex predators and generalist feeders is recommended. Such an evidence-based approach to bioindicator selection can significantly improve the ecological relevance, spatial comparability, and policy impact of marine litter monitoring efforts under the MSFD. By aligning species selection with both ecological function and contaminant exposure profiles, monitoring programs can deliver more accurate and actionable data to support marine environmental protection.