An IEO study quantifies the role of zooplankton in the microplastics cycle

A study by the Balearic Islands Oceanographic Centre of the Spanish Institute of Oceanography (IEO, CSIC) reveals that zooplankton continuously processes and transports hundreds of microplastics through the water column, transferring them to their predators.

According to information released by the IEO, CSIC, the research has recorded and measured for the first time, in real time, the speed at which microplastics pass through the digestive tract of copepods, a common North Atlantic species that is a key component of zooplankton.

Using these data, the amount of microplastics that these tiny organisms may be transporting to the ocean floor has been estimated.

According to the Institute, the analysis provides one of the clearest quantitative pictures to date of how zooplankton participates in the marine microplastics cycle.

To carry out the research, a team tracked individual microplastic particles from ingestion to excretion using real-time visualization techniques in the laboratory.

This analysis made it possible to measure intestinal transit time and ingestion intervals with great precision. Specifically, the team calculated that copepods could be driving microplastic fluxes on the order of about 271 particles per cubic meter of seawater per day in the western English Channel.

IEO, CSIC researchers noted that zooplankton is emerging as a key biological pathway for the transport of microplastics through marine ecosystems.

Given that there are estimated to be more than 125 trillion microplastic particles in the ocean, understanding how they move through ecosystems and food webs is essential to predicting their long-term consequences, they pointed out.

In particular, copepods occupy a central position in the marine food web and play a key role in the so-called “biological pump” by packaging carbon into fecal pellets that sink to the ocean floor.

Indeed, according to the Institute, copepods are the most abundant group of zooplankton in the ocean, meaning they can generate significant changes at the ecosystem scale.

In recent years, they added, copepods have been recognized as vectors of microplastics, although until now there had been no precise way to quantify how much plastic an individual copepod processes or how quickly.

Thus, the study offers a tool to integrate zooplankton behavior into ocean plastic transport models, reduce uncertainty about where microplastics accumulate over time, and improve risk assessments.

Likewise, they highlighted, the research helps scientists and policymakers identify critical areas of microplastic exposure and potential points of intervention.

The postdoctoral researcher and first author of the analysis, Valentina Fagiano, emphasized that by quantifying this flux it is possible to begin connecting what happens inside a single organism with how plastics are redistributed at the ecosystem scale.

“Our research shows that zooplankton ingests microplastics continuously, 24 hours a day,” she explained, adding that copepods not only come into contact with microplastics but act as “true mini biological pumps,” processing and repackaging them into their feces, which sink through the water column.

According to Fagiano, having realistic values for ingestion rates and intestinal transit time is essential for refining models that better predict where microplastics end up, which species are most exposed, and how this pollution interacts with other pressures affecting marine ecosystems.

The research was funded by the UK’s Natural Environment Research Council, and Fagiano’s stay was made possible thanks to a predoctoral FPI-CAIB grant co-funded by the regional government and the European Social Fund, as well as a mobility grant awarded by the regional government.