Plastic ingestion in European shags (Gulosus aristotelis): Temporal patterns and possible trophic transfer via Labridae prey in northern Spain

Marine plastic pollution is increasingly recognized as a major threat to marine ecosystems. Here, we investigate temporal patterns of diet composition and plastic ingestion in the European shag (Gulosus aristotelis), a generalist coastal predator closely associated with nearshore habitats and therefore well suited as a sentinel of coastal ecosystem change, over five non-consecutive years between 2006 and 2022. Over the study period, the species showed significant temporal shifts in prey use, although labrids consistently remained the dominant prey group. In contrast, the occurrence of plastic debris, mainly textile microfibers, remained stable across years, indicating a chronic and continuous exposure to this type of contamination. The coexistence of dietary variability and persistent plastic ingestion highlights the European shag's role as both an indicator of ecological change and a sentinel of long-term marine pollution. By combining detailed diet analysis with Fourier Transform Infrared (FTIR)-based identification of plastic polymers, our results provide additional evidence that microplastic exposure in European shags may partly occur through trophic transfer associated with dominant prey groups such as Labridae.