Small plastic detritus, commonly known as ‘microplastics’, are a widespread and ubiquitous contaminant of marine ecosystems across the globe. Reports widely indicate that marine biota, including mussels, worms, fish, and seabirds, ingest microplastics.
However, despite their vital ecological role in marine food-webs, the impact of microplastics on zooplankton remains under-researched.
What are Microplastics?
Microplastics consist of synthetic polymer products manufactured to be of small sizes, such as exfoliates in cosmetics, and those items derived from the fragmentation of larger plastic debris, for example, polyester fibers from fabrics, polyethylene fragments from plastic bags and polystyrene particles from buoys and floats. Typically, high-density plastics (e.g., polyvinyl chlorides, polyester) settle out of the water column, whereas low-density plastics (e.g., polyethylene, polystyrene) remain buoyant, although freshwater inputs, storms, and biofilm formation may result in vertical mixing. Floating plastic debris is susceptible to local and ocean currents resulting in higher-than-average waterborne microplastic concentrations in areas of confluence.
Microplastics are of environmental concern as their small size makes them available to a wide range of marine biota. Marine organisms, including amphipods, lugworms, barnacles, mussels, decapod crustaceans, seabirds, and fish, have been shown to ingest microplastics.
Ingested microplastics might obstruct feeding appendages, aggregate, and block the alimentary canal, limit the food intake of an organism or be translocated into the circulatory system. Further, microplastics may introduce toxicants to the organism: first, additives incorporated into a plastic during manufacture to improve its properties (e.g., phthalates for malleability and polybrominated diphenyl ethers (PDE) for heat resistance) might leach out of weathered plastic debris; second, the large surface area to volume ratio and hydrophobic properties of microplastics leave them susceptible to the accumulation of hydrophobic organic contaminants (HOCs) which could dissociate post-ingestion.
Microplastics in the Ocean
An estimated 10% of globally produced plastics enter our oceans, making plastic debris a pervasive and resilient marine environment pollutant.Larger plastic debris, including monofilament lines, plastic strapping, and plastic bags, can entangle, garrotte, or drown various marine wildlife, or become ingested by them.
There is compelling evidence that microplastics small plastic <5 mm in diameter also negatively impact upon marine biota.
Ingestion of Microplastics
We demonstrate here that zooplankton not only ingest microplastics but may also experience significant impacts as a result. We used bioimaging techniques to document ingestion, egestion, and adherence of microplastics in a range of zooplankton common to the northeast Atlantic, and employed feeding rate studies to determine the impact of plastic detritus on algal ingestion rates in copepods. Using fluorescence and coherent anti-Stokes Raman scattering (CARS) microscopy we identified that thirteen zooplankton taxa had the capacity to ingest 1.7-30.6 μm polystyrene beads, with uptake varying by taxa, life-stage, and bead-size.
Post-Ingestion of Microplastics
Post-ingestion, copepods egested fecal pellets laden with microplastics. We further observed microplastics adhered to the external carapace and appendages of exposed zooplankton. Exposure of the copepod Centropages typicus to natural assemblages of algae with and without microplastics showed that 7.3 μm microplastics (>4000 mL-1) significantly decreased algal feeding. Our findings imply that marine microplastic debris can negatively impact upon zooplankton function and health.
What Can We Do to Help?
We still have much to learn about microplastics; however, generally, the use of single-use plastics and plastic pollution are the primary known contributors to microplastics in our oceans. So, instead of using single-use plastics, instead invest in a metal re-usable straw, keep cup and other re-usable materials. For individuals eager to enact change, Aquatic Live Food offers the Manta Micro-Plastics Net, specifically designed to collect micro-plastics.
The additional benefit of this net is that it can collect surface zooplankton or phytoplankton for use in your home aquarium!