Zooplankton are the unsung heroes of the ocean, but they may be carrying a dark secret. These tiny creatures, which are the primary food source for many marine animals, are also transporting microplastics to the ocean depths. But here's where it gets controversial...
A new study reveals that copepods, a type of zooplankton, may be responsible for moving hundreds of microplastic particles per cubic meter of seawater down through the water column each day. This discovery is significant because it shows that microplastics are not just a surface ocean problem, but a deep-sea issue as well. And this is the part most people miss...
Copepods are the most numerous zooplankton in our ocean, dominating nearly every ocean region. Their staggering numbers mean that even small actions by individual animals, like ingesting microplastics, can collectively drive substantial ecosystem-level changes. This is a cause for concern, as it suggests that microplastics are not just accumulating on the surface, but are being actively transported to the depths by these tiny creatures.
The study, led by Dr. Valentina Fagiano and Dr. Matthew Cole, along with Dr. Rachel Coppock and Professor Penelope Lindeque, provides one of the clearest quantitative pictures to date of how microplastics are cycled by zooplankton in the ocean. Through real-time visualization, the researchers tracked individual microplastic particles as they were ingested and later expelled by copepods. This allowed them to measure gut passage time and ingestion interval with high precision.
The results showed that gut passage times clustered around a median of roughly 40 minutes, and were consistent across plastic shapes and food concentrations. This means that beads, fibres, and fragments all moved through the gut at similar speeds, and feeding conditions did not significantly slow or accelerate plastic throughput. By combining these measurements with realistic estimates of copepod abundance in the western English Channel, the team calculated that copepods could be driving microplastic fluxes on the order of about 271 particles per cubic meter of seawater per day.
This discovery has significant implications for ocean health. Copepod faecal pellets are negatively buoyant, meaning they sink down the water column. So, when microplastics are ingested by copepods and repackaged into faecal pellets, they should drop down the water column with them. This suggests that microplastics are being actively transported to the depths by these tiny creatures, and are accumulating in underlying sediment.
The study also highlights the need for more precise ways to gauge how much plastic an individual copepod processes and how fast. This will help scientists and policymakers identify hotspots of microplastic exposure and potential intervention points. By integrating zooplankton behaviour into ocean plastic transport models, reducing uncertainty around where microplastics accumulate over time, and improving risk assessments for ecologically or economically important regions, we can better predict where microplastics end up, which species are most exposed, and how this pollution interacts with other pressures on marine ecosystems.
In conclusion, this study shows that zooplankton, particularly copepods, are playing a crucial role in transporting microplastics to the ocean depths. This discovery is a wake-up call for the need to address the issue of microplastic pollution and its impact on ocean health. So, what do you think? Do you agree with the findings of this study? Or do you have a different interpretation? Share your thoughts in the comments below!
