Plastics are now widely distributed in the global ocean, serving as a new and serious contaminant for marine ecosystems. For instance, ingestion of small plastic detritus ( 0.1 μm ~ 5 mm), “microplastics” by fish, mussels and seabirds has been widely reported. A recent study (Cole et al., 2013) used fluorescence bioimaging techniques to show that microplastics are also ingested by a wide range of zooplanktons commonly found in the northeast Atlantic Ocean. Of course, there is no nutrient values in microplastics. So, the consumption of microplastics negatively impact zooplankton health. It also make them less hungry, and thus decreases their feeding of phytoplankton species such as copepods and diatoms. A new study published in Nature Communications (Kvale et al., 2021) now suggests that in the oceanic region where primary production is not limited by nutrient availability (e.g., coastal and equatorial upwelling regions) the reduced grazing of primary producers may cause a significant increase in export production (i.e., sinking of organic particles from surface to deeper ocean). This will in turn increase remineralization (organic to inorganic matters), which is carried out by heterotrophic bacteria through aerobic respiration, and thus consumes oxygen. The study used an intermediate complexity Earth system model to estimate that the additional remineralization caused by microplastics may have already reduced water column oxygen content by up to 10% from 1960 values. The study cautions a significant uncertainty in this their estimates. Nevertheless, this study provides an important implication that microplastics in the ocean and the consumption by zooplanktons may reshape the core structures of the global ocean primary production and biogeochemistry.
Image credit: https://pubs.acs.org/doi/10.1021/es400663f
Kvale, K., Prowe, A.E.F., Chien, CT. et al. Zooplankton grazing of microplastic can accelerate global loss of ocean oxygen. Nat. Commun. 12, 2358 (2021). https://doi.org/10.1038/s41467-021-22554-w
Cole, M. et al. 2013: Microplastic Ingestion by Zooplankton. Environ. Sci. Technol. 47, 6646–6655 (2013). https://doi.org/10.1021/es400663f