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Microalgae-mediated aggregation facilitates the vertical transport of microplastics: the role of Cylindrotheca closterium under simulated conditions
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In lab experiments, a type of algae called Cylindrotheca closterium clumped together with tiny polyethylene plastic particles of two sizes, forming aggregates that sank in water. Small plastic pieces got embedded inside the clumps, while larger pieces became coated with algae cells, showing that this algae can help carry microplastics downward in water.
Microplastics (MPs) released from aquaculture infrastructure represent a growing source of pollution in coastal environments, yet their fate in the presence of periphytic diatoms remains underexplored. This study investigates how the periphytic diatom Cylindrotheca closterium interacts with polyethylene (PE) MPs of two size classes (10-20 μm and 100-200 μm) under controlled laboratory conditions. Using 36-day time-series experiments, we examined cell attachment, aggregate formation, and sinking dynamics. C. closterium rapidly reached high biomass (>1.50 × 106 cells mL-1) and formed visible aggregates as early as day 11. Aggregation pathways differed by MP size: small particles became embedded within branched internal matrices, whereas large particles developed into dense, spherical flocs with external coatings of diatom cells. Large MPs served as nucleation cores, enabling higher MP incorporation per aggregate (mean 1.68-2.44 MPs) and generating attachment ratios exceeding 8.00 × 103 cells per particle in some treatments. Aggregate areas surpassed 1.7 × 105 μm2 in large-PE groups, and sinking velocities reached up to 3.70 mm s-1. Aggregate formation and downward transport occurred across all treatments, with distinct morphologies and performance depending on particle size and concentration. These results suggest that C. closterium promotes a robust pathway for MP aggregation and sedimentation through surface-mediated attachment rather than extensive extracellular matrix production. The size-dependent structural strategies highlight functional plasticity in capturing and retaining MPs. Overall, this study underscores the significant role of periphytic diatoms in regulating the environmental fate of aquaculture-derived MPs, providing new insight into biologically mediated removal processes in coastal ecosystems.
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Microplastic aggregation and sinking regulated by harmful alga Chattonella marina: Implications for vertical transport and resuspension
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Researchers experimentally studied how a toxic algal bloom species (Chattonella marina) affects the behavior of polyethylene and polypropylene microplastics in seawater, specifically their tendency to clump together and sink. They found that when the algae die and release intracellular material, it binds microplastics into large aggregates that sink faster — but these settled aggregates can resuspend again under cold conditions. This biological mechanism for transporting floating plastics to the seafloor has implications for where microplastics ultimately accumulate in marine ecosystems.
Microplastic interactions with freshwater microalgae: Hetero-aggregation and changes in plastic density appear strongly dependent on polymer type
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Researchers studied interactions between microplastics and freshwater microalgae, finding that microplastics can physically attach to algal cells to form hetero-aggregates, altering both particle behavior and algal physiology.
Impact of Heterosigma akashiwo on the environmental behavior of microplastics: Aggregation, sinking, and resuspension dynamics
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The harmful microalga Heterosigma akashiwo promoted aggregation and sinking of microplastics through extracellular polymeric substances (EPS) rather than direct cell attachment, with aggregation causing low-density PE spheres to sink following a logistic curve—demonstrating how harmful algal blooms can alter microplastic vertical distribution.
Phytoplankton community-driven regulation of microplastic sinking via marine gel formation and aggregation: mesocosm study under nutrient-enriched conditions
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Scientists found that tiny algae in ocean water can trap microplastics in sticky, gel-like clumps and drag them down to the seafloor, but how much this happens depends on which type of algae is blooming, not just how much algae is present. This matters because it means nutrient pollution (like fertilizer runoff) could actually influence where microplastics end up, potentially pulling them out of surface waters where fish and humans might be more likely to encounter them, or instead keeping them floating longer depending on the conditions.
Biological mediation of microplastic aggregation and sedimentation by a harmful dinoflagellate Prorocentrum minimum in a simulated marine environment
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A laboratory study found that the harmful dinoflagellate Prorocentrum minimum can form aggregates with polyethylene microplastics that significantly increase the microplastics' sinking rate — up to 22% of PE particles sank in algal cultures versus near zero in controls — suggesting that harmful algal blooms may act as a biological pump that transports surface microplastics to seafloor sediments. This biological-physical interaction means that the timing and location of algal blooms could shape where microplastics ultimately accumulate in coastal ecosystems.
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