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What is not seen: High levels of fibers below the sea surface revealed by a multisampler survey

Marine Pollution Bulletin 2026
Beatriz Rios-Fuster, Inmaculada Bernal-Mondejar, Carme Alomar, Estíbaliz Calleja-Setién, Natalia Sánchez-García, Salud Deudero

Summary

Scientists found that the tiny nets typically used to measure ocean plastic pollution massively underestimate the problem, when they sampled just below the surface instead of skimming the top, they found thousands of times more plastic fibers (likely from clothing and textiles) than surface samples suggested. This matters because these fibers are entering the marine food chain largely undetected, meaning our current methods may be dramatically underestimating how much plastic is in the seafood we eat and the water ecosystems we depend on.

Study Type Environmental

This study quantified microplastics and fibers in the upper 5 m of the water column and in sediments surrounding the Balearic Islands, assessing the effect of sampler mesh size, and filling the gaps on vertical microplastic distribution. Abundances of microplastic (excluding fibers) increased four orders of magnitude from the sea surface (manta trawl; 0.28 ± 0.59 MPs·m −3 ) to 5-m depth (Niskin bottles; 5433 ± 4191 MPs·m −3 ), and five orders with sediments (54,792 ± 130,705 MPs·m −3 ). Fiber abundances increased by six orders of magnitude from the sea surface (0.12 ± 0.14 fibers·m −3 ) to 5-m depth (118,258 ± 84,971 fibers·m −3 ), and with sediments (236,458 ± 288,773 fibers·m −3 ). Significant correlations with physicochemical parameters (e.g., turbidity) and potential sources (e.g., emissaries) demonstrated their contribution to the distribution of microplastics. These results highlight the need to consider subsurface layers when assessing microplastic pollution and suggest that nets underestimate fiber contamination in the ocean.

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