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Microalgae and associated ecological risks in the coastal plastisphere
Summary
Scientists found that floating ocean plastic acts like a magnet for tiny algae, hosting different and more diverse communities than the surrounding seawater—including several species known to produce harmful toxins. This matters because plastic debris could be helping harmful algae spread to new places or thrive in ways that affect seafood safety and coastal ecosystems, adding a new wrinkle to how ocean plastic pollution impacts marine life and, potentially, the food we eat.
Plastisphere-associated microorganisms add a microbial dimension to the impacts of plastic pollution. Yet microalgae, despite their central roles in coastal productivity, biodiversity, and harmful algal bloom dynamics, remain poorly characterized in the plastisphere. Here, using 92 paired samples of floating plastic debris and surrounding seawater, we aimed to reveal the ecological patterns of plastisphere-associated microalgae and their potential implications in coastal ecosystems. Plastisphere communities were significantly distinct from surrounding seawater communities and exhibited higher alpha-diversity. Diatoms, particularly taxa with benthic or attached ecological traits such as Navicula spp. , were enriched in the plastisphere. The plastisphere also harbored microalgal taxa typically reported from freshwater or terrestrial habitats, such as Mallomonas insignis . Compared with seawater communities, plastisphere microalgal communities showed weaker associations with measured physicochemical factors, suggesting that plastics may provide relatively buffered microhabitats. Using a self-constructed database of harmful and toxic microalgae, we identified 373 potentially harmful/toxic ASVs, including 14 detected exclusively in the plastisphere. Several ASVs affiliated with well-known harmful/toxic diatoms, such as Pseudo-nitzschia cuspidata and Skeletonema marinoi , were enriched in the plastisphere. Our findings indicate that plastic debris can selectively assemble and harbor microalgal communities, potentially influencing the ecology and biogeography of marine microalgae and introducing additional uncertainty into coastal ecosystem functioning.