Research conducted by scientists at Rissho University has uncovered significant evidence of marine plastic pollution affecting green sea turtles (Chelonia mydas) in the waters around the Ogasawara Islands in Japan. The study, published on January 11, 2026, in the journal PeerJ, highlights the alarming presence of plastic within the digestive tracts of these turtles, revealing that seven out of ten individuals examined had ingested plastic debris.
By employing a combination of genetic, isotopic, and plastic analyses, researchers determined that the plastics consumed by the turtles originated from regions beyond their known migratory paths. This finding underscores the impact of transboundary marine pollution on vulnerable marine species.
Understanding Sea Turtle Diets and Plastic Ingestion
Green sea turtles are known for their extensive migratory patterns, primarily inhabiting tropical and subtropical waters. In Japan, they nest in the Ogasawara Islands, which lie approximately 1,000 kilometers south of the main island. The turtles migrate from the Pacific coasts of Japan to these islands for mating and nesting.
According to Prof. Lee, who led the study, “During their long journey to Ogasawara Islands, the green turtles are likely to ingest and accumulate plastic distributed across a wide range of marine areas in various forms, including floating debris, sedimentary particles, and items mixed with seaweed.”
The research team analyzed the gut contents of ten captured turtles, discovering that their primary food source was macroalgae. Genetic analysis indicated that the turtles foraged in three key areas where specific seaweed species, such as Ectocarpus crouaniorum, Sargassum muticum, and Lobophora sp., were prevalent. Stable isotope analysis of carbon and nitrogen in the turtles’ muscle tissue suggested they may have also been feeding on drifting seaweed and gelatinous plankton during their migration.
Key Findings on Plastic Origins and Environmental Impact
The study revealed that the average number of plastic items found in the digestive tracts of the turtles was 9.2±8.5, with a range of 0 to 31 items per individual. Notably, macroplastics, measuring between 10 cm and 1 m in size, accounted for 56.5% of all plastic items detected. While microplastics (less than 5 mm) are commonly reported in marine organisms, this study emphasizes that sea turtles also ingest larger mesoplastics (between 5 mm and 2.5 cm) and macroplastics (between 2.5 cm and 1 m), which can have severe consequences for both the turtles and their ecosystems.
The findings suggest that the turtles likely mistook the ingested plastics for gelatinous prey, such as jellyfish and salpas, due to their association with large, drifting seaweeds. Analysis of printed characters on the plastic indicated origins from areas outside the turtles’ migratory range, further illustrating the transboundary nature of this pollution issue.
“This study demonstrates that plastic pollution is a transboundary issue,” Prof. Lee emphasized. “Efforts to reduce plastic pollution—including reduction in the production, use, and disposal of plastic products—must be pursued through international cooperation, alongside continued research.”
The implications of this research are profound, not only for green sea turtles but also for global marine ecosystems. Continued efforts to address marine plastic pollution are crucial to protect these vulnerable species and their habitats.
