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Plastic contamination is a global pervasive issue, extending from coastal areas and open oceans to polar regions and even the deep sea. Microplastic (MP) contamination in hydrothermal vents, which are known for their high biodiversity even under extreme conditions, has remained largely unexplored. Here, we present, for the first time, MP pollution in a deep-sea hydrothermal vent at one of the biodiversity hotspots─the Central Indian Ridge. Not only the environment (seawater: 2.08 ± 1.04 MPs/L, surface sediments: 0.57 ± 0.19 MP/g) but also all six major benthic species investigated were polluted by MPs. MPs mainly consisted of polypropylene, polyethylene terephthalate, and polystyrene fragments ≤100 μm and were characterized as being either transparent or white in color. Remarkably, bioaccumulation and even biomagnification of microplastics were observed in the top predators of the ecosystem, such as squat lobsters (14.25 ± 4.65 MPs/individual) and vent crabs (14.00 ± 2.16 MPs/individual), since they contained more MPs than animals at lower trophic levels (e.g., mussels and snails, 1.75-6.00 average MPs/individuals). These findings reveal MP contamination of an ecosystem in a hydrothermal vent, thereby suggesting that their accumulation and magnification can occur in top-level animals, even within remote and extreme environments.

Microplastics (MPs) are found in every ocean and are frequently ingested by marine animals. This study analyzed MPs in the stomachs and intestines of 12 large marine animals comprising one fin whale (Balaenoptera physalus), seven finless porpoises (Neophocaena asiaeorientalis), two loggerhead turtles (Caretta caretta), one Indo-Pacific bottlenose dolphin (Tursiops aduncus), and one common dolphin (Delphinus delphis) that were stranded off the Republic of Korea between 2019 and 2021. MPs were detected with a mean abundance of 3.42 ± 3.2 items/g and were predominantly of transparent-white, fragment-shaped polypropylene smaller than 200 μm. The abundance of MPs found did not correlate with the biological information (maturity, body length) of the finless porpoises and there were no significant differences in the abundance of MPs between the stomachs and intestines. These results cannot accurately assess the impact of MPs on large marine animals, so further studies are necessary to understand how MPs can potentially affect them. [Display omitted] • Microplastics were examined in five species of large marine animals. • Polypropylene and transparent-white fragments of microplastics predominated. • The abundance of microplastics did not correlate with the porpoises' size and age. • >68 % of the microplastics found were smaller than 200 μm. [ABSTRACT FROM AUTHOR]