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Microplastic aggregation and sinking mediated by the harmful dinoflagellate Prorocentrum minimum under simulated marine conditions
Summary
Scientists found that a common type of harmful algae can grab tiny plastic particles and pull them down to the ocean floor, which could remove billions of plastic pieces from coastal waters each year. This is important because it shows how nature might help clean up some plastic pollution in areas where people swim and get seafood. However, we still need to understand where these plastics end up and whether they could eventually make their way back into our food chain.
Coastal estuaries are recognized as hotspots for both microplastics (MPs) and harmful algal blooms (HABs); however, the role of dinoflagellates in facilitating MP sinking remains poorly understood. In this study, we investigated aggregate formation between dinoflagellate Prorocentrum minimum and polyethylene (PE; densities of 1.0 and 1.4 g cm⁻³, particle size 10–20 µm) and polypropylene (PP; density 0.91 g cm⁻³, particle size 45–75 µm) using roller–shaker incubations. Phytoplankton growth, aggregate morphology, sinking velocity, and aggregate stability were evaluated through microscopic observations and statistical analyses. Growth of P. minimum was not inhibited by MP exposure; notably, PE treatments exhibited significantly higher biomass than the control during both the exponential and stationary phases (p < 0.05). Aggregates first appeared on Day 10 and progressively incorporated MPs and fragmented thecal plates. The sinking ratio of PE1.0 particles increased steadily, reaching approximately 22% (R² = 0.96, p < 0.05), whereas PP particles exhibited negligible sedimentation (70 days) revealed no evidence of aggregate resuspension. Collectively, these results demonstrate that thecate morphology constrains MP export efficiency relative to extracellular polymeric substance (EPS)-rich raphidophytes. Nevertheless, scaling our experimental results suggests that Prorocentrum blooms may export on the order of 10¹⁰ MP particles annually, underscoring the importance of species-specific traits as key regulators of MP vertical transport and ultimate fate in coastal ecosystems.
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