Study on the seasonal impact of marine litter on seabirds in the Ebro Delta

Photo:Odei Garcia-Garin

A new study published in the journal Science of the Total Environment highlights the risks that marine plastic waste poses to birds in the Delta de l’Ebre. The study, led by researchers from the Biodiversity Research Institute of the University of Barcelona, has analyzed the seasonal distribution of plastic waste and its potential impact on three species of terns (family Laridae, subfamily Sterninae).

Marine litter, including floating marine macro-waste (FMML) and microplastic (MP), pose a major threat to marine ecosystems. This work investigates the seasonal distribution of FMML and MP in the Delta de l’Ebre, a key Mediterranean wetland, and evaluates the potential risk for three species of tern that depend on the area for their feeding and reproduction.

Seasonal sampling was carried out between October 2021 and June 2022, using drones and trawl nets to quantify the abundance of marine litter. The density of terns was estimated by direct observation in linear transects from a ship.

The results revealed seasonal peaks in FMML and MP densities, with the highest concentrations in autumn and spring. These temporal variations are probably influenced by the flow of the Ebre river and the watering runoff. Risk assessment maps identified high-risk areas where the density of terns overlapped with high concentration points of FMML and MP. This suggests possible threats of blockage, ingestion and trophic transfer of pollutants. Overall, these results highlight the relevance of seasonality and spatial risk assessment when evaluating the exposure of wildlife and the environment to marine litter.

This study not only improves our understanding of the impacts of marine litter in the Delta de l’Ebre, but also provides essential data to inform evidence-based policies and management strategies aimed at protecting vulnerable species across the Mediterranean.

Odei Garcia-Garin, first author of the study, highlighted: "Our results show that plastic waste management must take seasonal variations into account in order to be effective. This study provides a solid basis for the implementation of specific conservation measures for seabirds in the Ebro Delta."

Reference article:

Odei Garcia-Garin, Mireia Burzón, Luis Cardona, Raül Ramos. Plastic exposure risk for costal seabirds varies seasonally with freshwater runoff. Science of The Total Environment, Volume 976, 2025, 179316, ISSN 0048-9697,https://doi.org/10.1016/j.scitotenv.2025.179316