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Microplastics Alter the Properties and Sinking Rates of Zooplankton Faecal Pellets
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Researchers found that when zooplankton ingest microplastics, the plastic particles become embedded in their fecal pellets, making those pellets smaller, less dense, and slower to sink. Since these pellets normally help transport carbon from the ocean surface to the deep sea as part of the biological pump, altered sinking rates could disrupt this important carbon cycle process. The study reveals a previously unrecognized way that microplastic pollution could affect ocean chemistry and climate regulation.
Plastic debris is a widespread contaminant, prevalent in aquatic ecosystems across the globe. Zooplankton readily ingest microscopic plastic (microplastic, < 1 mm), which are later egested within their faecal pellets. These pellets are a source of food for marine organisms, and contribute to the oceanic vertical flux of particulate organic matter as part of the biological pump. The effects of microplastics on faecal pellet properties are currently unknown. Here we test the hypotheses that (1) faecal pellets are a vector for transport of microplastics, (2) polystyrene microplastics can alter the properties and sinking rates of zooplankton egests and, (3) faecal pellets can facilitate the transfer of plastics to coprophagous biota. Following exposure to 20.6 μm polystyrene microplastics (1000 microplastics mL(-1)) and natural prey (∼1650 algae mL(-1)) the copepod Calanus helgolandicus egested faecal pellets with significantly (P < 0.001) reduced densities, a 2.25-fold reduction in sinking rates, and a higher propensity for fragmentation. We further show that microplastics, encapsulated within egests of the copepod Centropages typicus, could be transferred to C. helgolandicus via coprophagy. Our results support the proposal that sinking faecal matter represents a mechanism by which floating plastics can be vertically transported away from surface waters.
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Researchers found that microplastic ingestion by salps (Salpa fusiformis) at environmentally realistic concentrations reduced the density and sinking speed of their fecal pellets, suggesting that widespread microplastic contamination could impair the biological pump's ability to sequester carbon in the deep ocean.
Modeling the Vertical Transport of Copepod Fecal Particles under Nano/Microplastic Exposure
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Researchers studied how nano- and microplastics affect the fecal pellets produced by tiny marine copepods, which play a crucial role in transporting carbon from the ocean surface to deeper waters. They found that plastic particles reduced both the size and production rate of fecal pellets, and a fluid dynamics model showed this would slow their sinking speed and reduce vertical carbon transport. The study suggests that widespread microplastic pollution could interfere with the ocean's ability to sequester carbon.
The faecal microplastic pump: Zooplankton efficiently transport microplastics to the ocean depths
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Researchers quantified how zooplankton grazing and sinking fecal pellets drive the bulk of microplastic export below 1000 meters in the open ocean, identifying this "fecal pump" as a critical pathway for deep-sea microplastic sequestration that outweighs polymer-density-driven sinking in offshore waters.
Microplastics may reduce the efficiency of the biological carbon pump by decreasing the settling velocity and carbon content of marine snow
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Researchers found that microplastic fibers reduce the efficiency of the ocean's biological carbon pump by slowing the sinking of marine snow — clumps of organic material that carry carbon to the deep sea. This suggests that microplastic pollution could interfere with a key natural climate regulation mechanism by altering how carbon moves from surface waters to the ocean floor.
Regionally disparate ecological responses to microplastic slowing of faecal pellets yields coherent carbon cycle response
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This study modeled how microplastics slow the sinking of zooplankton fecal pellets and found that, despite regional variation in the ecological response, the net effect on the ocean carbon pump is a coherent reduction in carbon export to the deep ocean across different ocean regions.
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