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From seafloor litter to living substrate: A first assessment of litter composition and plastic-associated fouling communities in the Gulf of Thailand

Estuarine Coastal and Shelf Science 2026
Suppakarn Jandang, Haruka Nakano, María Belén Alfonso, Nopphawit Phinchan, Udomsak Darumas, Keiichi Uchida, Hisayuki Arakawa, Nathacha Changphetphol, Sukchai Arnupapboon, Prakrit Noppradit, Voranop Viyakarn, Suchana Chavanich, Atsuhiko Isobe

Summary

Scientists surveying the seafloor in the Gulf of Thailand found it littered mostly with plastic—sheets, string, rope, and fishing gear—much of it clustered near river mouths, showing that trash from land is flowing into the ocean and settling on the bottom. This plastic doesn't just sit there; it becomes a surface where marine organisms grow, and as it breaks down over time, it likely contributes to the microplastics that can enter the seafood we eat. The findings matter because they help identify pollution hotspots and support better strategies to stop plastic waste before it reaches the ocean and, eventually, our din

Study Type Environmental

Seafloor litter is an increasing environmental concern in marine ecosystems, yet its composition and ecological interactions in many regions remain poorly characterized. We conducted trawl surveys at 12 stations spanning the Upper to Middle Gulf of Thailand to provide the first comprehensive assessment of seafloor litter and associated fouling communities there. Litter densities ranged from 132.7 to 484.2 items km –2 , with a mean density of 257.0 ± 112.1 items km –2 , and from 0.2–165.4 kg km –2 , with a median density of 2.9 kg km –2 (IQR: 1.2-7.6 kg km –2 ). The highest litter densities were observed at stations located near major river mouths in the Upper Gulf of Thailand, which suggests that riverine inputs may contribute to spatial patterns of litter accumulation. Plastic debris dominated the assemblage (85.7%), with plastic sheets (31.2%), string (20.4%), ropes (12.8%), and fishing gear and lines (12.8%) comprising the largest fractions. Polymer analysis indicates a predominance of polyethylene (40.0%), polypropylene (34.0%), and nylon (13.2%). The mean percent cover on plastic litter was highest for bryozoans (75.4%); however, fouling community composition did not differ significantly among sampling stations, litter categories, or polymer types. This study also reports the first record of a chitinous tube remnant attached to seafloor litter, highlighting the potential for submerged debris to serve as a substrate for opportunistic and potentially harmful taxa. Overall, these findings provide an important baseline dataset for Southeast Asia, improve our understanding of litter accumulation and biofouling patterns, and support the development of integrated mitigation strategies addressing both terrestrial and marine sources of pollution.

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