Two decades of marine litter surveys on the North Atlantic Iberian coast: a spatial and temporal analysis of the OSPAR dataset for Portugal and Spain.

The OSPAR litter program was promoted to investigate the abundance and types of the most common macro-litter items on European beaches. This baseline analyses the data collected under the program on the North Atlantic Iberian coast between 2002 and 2020. The dataset includes surveys conducted on 25 beaches along the entire continental Portuguese coastline, as well as the shores of the Galicia and Andalusia regions of Spain. Considering the data grouped on the basis of the seven coastal regions, the median litter abundance ranged from 90 to 259 items/100 m, reflecting an average increase of 9 items/100 m per year between 2002 and 2020. The beaches in the Lisbon and Central regions of Portugal have consistently exhibited the highest levels of pollution along the North Atlantic Iberian coast over the past eight years. The estimation of litter bulk weight, based on the last four years of surveys, indicated that the highest values were in the Central region of Portugal during winter (17 kg/100 m) and spring (13 kg/100 m), while in the Lisbon region during summer (10 kg/100 m) and autumn (18 kg/100 m). An analysis of individual beaches revealed that the median litter bulk weight ranged from 25 to 30 kg/100 m during winter and spring, while more than half of the beaches exhibited median weights of <5 kg/100 m throughout the year. Over the 19 years of monitoring, the proportion of plastics increased from 43 % to 68 %, while the proportion of fishing-related items decreased from 20 % to 14 %.