Mangrove ecosystems are ecologically important coastal habitats, yet data on microplastic (MP) contamination along Bahrain’s coasts remain scarce. This study investigated the abundance, characteristics, and ecological risks of MPs in sediments from four mangrove sites (12 stations) collected in 2025. MPs were extracted via density separation and characterized by size, shape, color, and polymer composition using Raman spectroscopy; ecological risk was assessed using the Pollution Load Index, Polymer Hazard Index, and Potential Ecological Risk Index. MPs were detected at all stations, with abundances ranging from 533.33 ± 2.08 to 958.33 ± 6.5 particles/kg dry weight. Fragments were dominant in shape, and black was the dominant color. Particles < 10 μm and 10–30 μm were the most abundant size classes, with the sub-10 μm fraction, uncharacterized in Gulf mangrove ecosystems, suggesting that current methods underestimate MP abundance and associated ecological risk. Given their high surface reactivity, adsorption capacity, and potential root uptake, these ultrafine particles highlight the need for standardized, high resolution detection methods. Nylon-6 predominated all sampling sites, irrespective of their onshore or offshore setting, indicating common and persistent anthropogenic sources. Although ecological risk indices suggested an overall low-to-moderate environmental risk, the ubiquitous occurrence of MPs throughout Bahrain’s mangrove sediments raises concern regarding their long-term ecological implication. These findings provide a robust baseline for future spatiotemporal monitoring, refined ecological risk assessments, and the formation of targeted management strategies to safeguard coastal ecosystems.

This study provides the first comprehensive assessment of microplastic (MP) contamination within oyster bed ecosystems of the Kingdom of Bahrain. Sediment, water, and oyster samples were collected from six sites representing diverse environmental conditions. Raman spectroscopy identified the presence of 12 distinct polymer types, with polypropylene (PP), polyurethane (PU), poly(ethylene terephthalate)/diamine/multi-walled carbon nanotube (PET/diamine/MWCNT), and fluorinated ethylene propylene (FEP) being the most prevalent. MPs occurred predominantly as fragments, films, and pellets, with black being the most common color across all matrices. MP abundances ranged from 750 to 1850 MPs/kg dry weight in sediments, 2100–9600 MPs/L in water, and 1.78–5.25 MPs/individual in oysters, with particles (<50 µm) most frequent in oyster tissues. Although spatial variation was evident across regions, detected polymers included types associated with known ecotoxicological risks. No significant correlation was observed between sediment grain size and MP abundance, suggesting that additional hydrodynamic or anthropogenic factors may influence MP distribution. Overall, this study provides critical baseline data on MP contamination in Bahrain’s marine environments and highlights the need for continued monitoring to assess potential risks to marine ecosystems and seafood safety. It also contributes to the limited understanding of MPs in the Arabian Gulf, informing future monitoring, conservation and policy initiatives that support long-term environmental sustainability.