Microplastics and Zooplankton

With the long awaited Blue Planet 2 series around the corner, its presenter David Attenborough describes the heart-breaking tale of watching a breeding albatross mistakenly trying to feed plastic to her chick 1,2. Unfortunately these events are not uncommon, but dumping plastic into our oceans may be having another serious and yet unseen consequence.

Take a beaker of sea-water, put it under a microscope, and you will see it polluted with tiny plastic particles, under 5mm in diameter, called microplastics. These small plastics are produced specifically, such as for personal hygiene products, or result from the degradation of larger debris. Microplastics are now considered ubiquitous across the marine environment and they have been transported, via ocean currents, to even the remotest regions. Including arctic waters, isolated islands and to the bottom of our oceans 3.

Look at the beaker again, and you will see it is also teaming with microscopic animals called zooplankton. These organisms are a crucial energy transfer mechanism between marine trophic levels as they graze on bacteria and phytoplankton, and themselves are predated on by planktivorous species. They also play a role in marine nutrient cycling as their faecal pellets drift down through the water column, forming a component of the marine snow, providing a nutrient input into deeper waters 4.

Given their importance, it is worrying that research is now showing that the presence of microplastics in the marine environment is negatively impacting the zooplankton community.

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Shampoo containing relatively large plastic microbeads

Several zooplankton taxa have been observed ingesting microplastics, including the ecologically important copepods, which may not be able to differentiate between them and similar sized prey 3,5,6. Cole et al. (2015) for example showed that the copepod Calanus helgolandicus would ingest 20µm diameter polystyrene microbeads via selective filter feeding, even in the presence of their algal prey. After microbead ingestion, C. helgolandicus consumed significantly smaller, and therefore less, algal cells. During reproduction, exposed individuals also suffered from producing smaller eggs with lower chances of hatching successfully 6. Research such as this suggests the physical effects of polystyrene microbeads are inhibitory to the behaviour and individual fitness of zooplankton, or at least, copepods. Perhaps future research should investigate their impact on alternative zooplankton taxa, and their potential chemical effects on the zooplanktons’ endocrine system by using less stable plastic compounds. Additionally, given the fact that exposed C. helgolandicus were shown to produce more eggs, even though they were smaller, it might be worthwhile investigating the influence of microplastics on overall reproductive fitness. Possibly over multiple generations and or at a population level. Nevertheless, the findings of this research are incredibly concerning, especially as it didn’t consider the influence of smaller microplastics that can adhere to the external surfaces of zooplankton. An issue that is likely to only add to their negative impact.

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An example Copepod

If these findings are found to apply to other zooplankton taxa, something that research is continuing to address, microplastic pollution may reduce the abundance of zooplankton in the marine environment. This will reduce prey availability for planktivorous species, which will then have a knock-on effect for the predators at higher trophic levels. A sequence of events known as a trophic cascade. Exposed zooplankton also eject faecal pellets laden with microplastics, which may influence their role in marine nutrient cycling as they sink at a slower rate, and are more likely to be consumed by other organisms in the water column. Potentially reducing the amount of nutrients reaching the deeper ecosystems. The pellets that do reach bottom however may serve to pollute these areas with microplastics as well 7.

As human industrial activity continues to intensify, plastic production is likely to increase and we are only now beginning to understand the severity of microplastic pollution and its implications on the marine ecosystem. Moves such as the UK banning the use of microbeads in cosmetic and personal products is certainly a positive move, but, I fear this is not enough 8. Perhaps better waste management and the development of biodegradable materials are also necessary. As for the plastic already polluting our oceans, who knows? Perhaps the possibility of using plastic eating enzymes/bacteria in the near future will act as a solution 9, but regardless, we must start taking responsibility for protecting our oceans.

  1. Marris, S (2017, September 15th). Sir David Attenborough: Sea plastic’s impact on albatross is ‘heartbreaking’. SkyNews. http://news.sky.com/story/sir-david-attenborough-sea-plastics-impact-on-albatross-is-heartbreaking-11052475
  2. Harvey, F (2017, September 25th). David Attenborough on the scourge of the oceans: ‘I remember being told plastic doesn’t decay, it’s wonderful’. The Guardian. https://www.theguardian.com/tv-and-radio/2017/sep/25/david-attenborough-on-the-scourge-of-the-oceans-i-remember-being-told-plastic-doesnt-decay-its-wonderful
  3. Auta H.S., Emenike C.U., Fauziah S.H. (2017). Distribution and importance of microplastics in the marine environment: A review of the sources, fate, effects, and potential solutions. Environment International 102 165-176. http://www.sciencedirect.com/science/article/pii/S016041201631011X
  4. Turner J.T. (2002). Zooplankton fecal pellets, marine snow and sinking phytoplankton blooms. Aquat Microb Ecol 27 57–102. http://www.int-res.com/abstracts/ame/v27/n1/p57-102/
  5. Cole M., Lindeque P., Fileman E., Halsband C., Goodhead R., Moger J., Galloway T.S. (2013). Microplastic Ingestion by Zooplankton. Environ Sci Technol 47 6646–6655. http://pubs.acs.org/doi/abs/10.1021/es400663f
  6. Cole M., Lindeque P., Fileman E., Halsband C., Galloway T.S. (2015). The Impact of Polystyrene Microplastics on Feeding, Function and Fecundity in the Marine Copepod Calanus helgolandicus. Environ Sci Technol 49 1130–1137. http://pubs.acs.org/doi/abs/10.1021/es504525u
  7. Cole M., Lindeque P., Fileman E., Clark J., Lewis C., Halsband C., Galloway T.S. (2016). Microplastics Alter the Properties and Sinking Rates of Zooplankton Faecal Pellets. Environ Sci Technol 50 3239–3246. http://pubs.acs.org/doi/abs/10.1021/acs.est.5b05905
  8. BBC News (2016, September 3rd). Plastic microbeads to be banned by 2017, UK government pledges. BBC http://www.bbc.co.uk/news/uk-37263087
  9. Coghlan A. (2016, March 10th). Bacteria found to eat PET plastics could help do the recycling. New Scientist. https://www.newscientist.com/article/2080279-bacteria-found-to-eat-pet-plastics-could-help-do-the-recycling/

 

Author: Luke Williams

A graduate of Zoology (MBiolSci) from the University of Sheffield with an interest in marine conservation and wider ecological issues.

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