A shocking reality is unfolding beneath the ocean's surface, and it's time to dive into the depths of this critical issue. The ocean's tiny inhabitants, zooplankton, are unknowingly transporting microplastics to the ocean's depths, posing a serious threat to marine ecosystems.
With an estimated 125 trillion microplastic particles already accumulated in our oceans, understanding this phenomenon is crucial for predicting the long-term health of our oceans. Among these zooplankton, copepods stand out as the most abundant, dominating nearly every ocean region, from the surface to the deep sea.
New research, led by Dr. Valentina Fagiano and a team of experts from PML and COB-IEO-CSIC, has revealed a startling discovery. Copepods, it seems, are transporting hundreds of microplastic particles per cubic meter of seawater down through the water column daily. This research, published in the Journal of Hazardous Materials, provides a clear quantitative picture of how zooplankton cycle microplastics in the ocean.
But here's where it gets controversial: copepods, a vital part of the marine food web, are not just encountering microplastics; they're actively ingesting and processing them. These tiny creatures, which feed on microalgae, are then consumed by fish, seabirds, and marine mammals, potentially passing on the microplastics they've ingested. And this is the part most people miss: copepods also drive the 'biological pump', packaging carbon into fecal pellets that sink into deeper waters, taking the microplastics with them.
Through their study, the researchers collected a common North Atlantic copepod species, Calanus helgolandicus, using a fine-mesh plankton net. In the lab, these copepods were exposed to different types of microplastics: fluorescent polystyrene beads, polyamide fibers, and fragments. By tracking individual microplastic particles in real-time, the researchers measured gut passage time and ingestion interval with high precision.
The results were eye-opening. Gut passage times averaged around 40 minutes, consistent across plastic shapes and food concentrations. This means that regardless of the type of microplastic or the copepod's feeding conditions, the plastics moved through their guts at a similar pace.
By combining these measurements with estimates of copepod abundance in the western English Channel, the team calculated that copepods could be driving microplastic fluxes of approximately 271 particles per cubic meter of seawater per day in that region.
Dr. Matthew Cole, a senior marine ecologist and ecotoxicologist at PML, explains, "Copepod fecal pellets sink down the water column, so when microplastics are ingested and then repackaged into these pellets, they drop down with them."
Dr. Rachel Coppock, a Marine Ecologist at PML, adds, "Microplastic pollution is not just a surface ocean problem. Zooplankton are constantly moving plastics through the water column and into the food web. Copepods are like mini biological pumps, processing and transporting microplastics day after day."
Professor Penelope Lindeque highlights the broader implications, "This process is like a microplastic plumbing system and a microplastic food delivery service. Zooplankton are sinking microplastics and passing them up the food chain."
This research provides a much-needed quantitative framework to integrate zooplankton behavior into ocean plastic transport models. It helps reduce uncertainty about microplastic accumulation over time and improves risk assessments for ecologically and economically important regions. Ultimately, it aids scientists and policymakers in identifying hotspots of microplastic exposure and potential intervention points.
Dr. Fagiano, the lead author, emphasizes, "By quantifying this flux, we can link what happens inside a single animal to the redistribution of plastics across entire ecosystems. Our research shows that zooplankton are constantly ingesting microplastics. They're like mini biological pumps, repackaging microplastics into their feces, which sink and accumulate in sediments."
Having realistic data on ingestion and gut passage is crucial for computer models. It allows us to predict where microplastics end up, identify the most exposed species, and understand how this pollution interacts with other marine ecosystem pressures.
This collaboration between Dr. Fagiano and the PML team showcases the value of international mentoring and training. It combines PML's expertise in zooplankton ecology and microplastic methods with Dr. Fagiano's specialization in real-time visualization and flux quantification.
So, what do you think? Are you surprised by the role of zooplankton in transporting microplastics? How do you think we can address this issue to protect our oceans? We'd love to hear your thoughts in the comments below!
