Research conducted by scientists from Rissho University has revealed significant evidence of cross-regional marine plastic pollution affecting green sea turtles in the waters surrounding the Ogasawara Islands, Japan. The study, published in the journal PeerJ on January 11, 2026, found plastics in the digestive tracts of seven out of ten turtles examined, indicating the influence of transboundary marine pollution.
The research team used a combination of genetic, isotopic, and plastic analyses to trace the origins of the ingested plastics. The findings suggest that the plastics did not come from the turtles’ immediate migratory range, underscoring a concerning trend of global marine pollution. “This study demonstrates that plastic pollution is a transboundary issue,” stated Professor Lee, one of the lead researchers.
Plastics pose a serious threat to marine life, including various organisms such as pelagic fishes, whales, and zooplankton. Among these, sea turtles are particularly vulnerable. The ingestion of plastics by these turtles primarily occurs through two pathways: the nonselective consumption of plastics mixed with their natural food items like algae and the selective consumption of plastics resembling jellyfish, one of their typical prey. Despite this, comprehensive data on the dietary habits of sea turtles remain scarce.
Migration Patterns and Feeding Habits of Green Turtles
Green sea turtles are distributed globally, predominantly in tropical and subtropical waters. In Japan, they nest on the Ogasawara Islands, located approximately 1,000 kilometers south of the main island. These turtles migrate from the Pacific coasts of the Japanese mainland to the Ogasawara Islands for mating and nesting.
During this journey, they are likely to consume plastics found in various forms, including floating debris and items mixed with seaweed. “To estimate the factors influencing plastic ingestion and the origin of the ingested plastics, we integrated morphological and genetic analysis of gut contents with isotopic and plastic analyses of ten green turtles captured in the Ogasawara Islands,” Professor Lee explained.
Findings on Plastic Ingestion and Its Origins
At the time of capture, the primary food source for the turtles was macroalgae. DNA analysis indicated that their feeding grounds could be traced to three distinct locations where preferred seaweed species, including Ectocarpus crouaniorum, Sargassum muticum, and Lobophora sp., are prevalent. The stable isotope ratios of carbon and nitrogen in muscle tissue, together with DNA analysis, suggest that the turtles may have consumed drifting seaweed and gelatinous plankton during their migration toward the Ogasawara Islands.
The study reported an average of 9.2 plastic items per turtle, with a range from zero to thirty-one items. Notably, 56.5% of the plastics detected were macroplastics, which are larger than 10 cm² and can have more severe impacts on marine organisms and ecosystems compared to microplastics. While most plastics found in marine organisms are microplastics (less than 5 mm), green sea turtles are known to ingest larger mesoplastics (between 5 mm and 2.5 cm) and macroplastics (between 2.5 cm and 1 m).
The study suggests that the turtles likely mistook meso- and macroplastics for gelatinous plankton, such as jellyfish and salpas, due to their association with large and drifting seaweeds. Analysis of printed characters found on the ingested plastics indicates that they originated from regions beyond the turtles’ migratory range, highlighting the need for international cooperation in addressing marine plastic pollution.
Professor Lee emphasized the importance of ongoing efforts to reduce plastic pollution, stating, “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 extend beyond the Ogasawara Islands, signaling a pressing need for concerted global action to mitigate the effects of plastic pollution on marine ecosystems.
