Assessment of Seafloor Litter in the Gulf of Thailand Using Benthic Trawls: Composition, Distribution, and Implications for Plastic Pollution Management

Plastic waste reduction is a global challenge, so it is crucial to examine specific regions that contribute significantly to the release of plastic waste. We used benthic trawls to examine seafloor litter in the Gulf of Thailand (GoT), which is bordered by several ASEAN (Association of Southeast Asian Nations) countries where plastic emissions are considered significant. The amounts of seafloor litter in October 2023 and April 2024 were 262.9 and 245.7 items km –2 , respectively, with plastic sheets and plastic bags identified as the dominant types. This abundance is lower than that reported in global data. A mass comparison indicates that, if the seafloor acted as a permanent sink, no more than a few percent of the discharged plastic waste would be retained there. This may reflect genuinely lower emissions than initially estimated, active removal and redistribution of litter, or methodological underestimation inherent to trawl surveys compared with imaging analyses; direct methodological intercomparison (e.g., simultaneous ROV-based surveys) is therefore needed. Of the seafloor litter, single-use plastics and fishing- and maritime-related litter accounted for 22.8% and 36.4% of the total amount, respectively. The standing stock of seafloor litter shows no clear seasonal pattern, unlike that of floating plastics, although this does not exclude seasonality in the underlying fluxes. Based on these results, this study provides important insights for advancing marine debris countermeasures in ASEAN countries.