Plastic pollution in Leeward, Moorea and Cook islands (South Pacific): A baseline study

Plastic pollution is increasingly affecting the South Pacific, including remote islands and coastal regions of Small Island Developing States (SIDS), yet data remain sparse in many areas. This baseline study presents original data on beach macrolitter and microplastics in surface waters and sediments across six islands of French Polynesia (Moorea, Bora Bora, Tahaa) and the Cook Islands (Aitutaki, Rarotonga), collected during a cruise in 2024. Beach surveys revealed high plastic contamination on most sites, with macroplastics (size >2.5 cm) densities ranging from 18 to 58 items/100 m, exceeding European threshold values (e.g. 22 items/100 m) on majority of sampled beaches. Single-use plastics and plastic fragments dominated litter, with local sources such as tourism and coastal activities clearly identifiable. Surface microplastics (315 μm-5 mm) were found at low densities, ranging from 0 to 4668 particles/km², confirming relatively low contamination in surface waters. Only 17 particles were detected from 8 manta net tows. Sediment and beach microplastic analysis yielded very limited results, with microplastics found at only two sites (Huahine and Rarotonga), dominated by fragments and colored fibers. These results suggest localized contamination linked to urbanization and tourism rather than widespread oceanic inputs. Despite methodological limitations due to the cruise format, this study contributes rare data from under-sampled regions, supporting long-term monitoring efforts and informing future policy and mitigation actions. The results underline the need to improve regional waste management, which will be beneficial for local societies largely based on tourism.