Microplastics in the marine environment is a globally
anthropogenic issue and can threaten ecosystems in a variety of ways. It is
well understood that these plastics are consumed by marine life and can build
up through the food chain when higher trophic organisms consume prey who have
already ingested microplastics. This can have detrimental effects on the health
of organisms, such as reduced feeding habits, less energy and increased immune
response. Microplastics can also facilitate the transportation of organic
pollutants and toxic materials such as polycyclic aromatic hydrocarbons and
hydrocarbon petroleum residues into deeper waters.
Zooplankton, such as copepods are ecologically significant
with respect to their abundance throughout the world’s oceans and the
biological processes they perform. They can also provide important information
on ocean pollutants and acidification in a wide spectrum. Copepods faecal
pellets are important for transportation of particulate organic matter (POM),
carbon and nutrients from the surface to the benthos. Copepods are marine
nutrient recyclers and play an important role in consuming, digesting,
repackaging and excreting POM. However, when copepods ingest microplastics as
prey, this paper asks the important ecological question, what are the impacts microplastics have on copepod faecal pellets and the environment around them?
Previous literature into microplastics in zooplankton has
been limited, with papers mainly focusing on the interactions in surface
waters. However this paper explores for the first time, by demonstrating
sinking rates, that there can be an impact in deeper waters.
This study used marine copepods Calanus helgolandicus and Centropages typicus, allowing them to consume either natural prey (consisting of
phyto-flagellates, diatoms and coccolithophores); cultured prey (the
unicellular haptophyte Isochrysis galbana)
and microplastics. The representative microplastics used in this paper are 20.6
μm polystyrene and 7.3 μm fluorescent polystyrene beads which is one of the
most commonly manufactured polymers in the world. The concentrations used (1000
microplastics mL-1) are higher than in previous literature, however these
concentrations were decided based on concentrations consistent with areas of
high contamination in open water.
Both species readily ingested the microplastics, which were
encapsulated in the gut and all pellets, including those with microplastics
sank. The study showed that incorporation of microplastics into the pellets did
not impact the size or volume of the pellets; however, plastic treatments
showed to have a much lower density and significantly slower sinking rates
(38.3 ± 2.6 m day−1) allowing pellets to become more susceptible to being eaten
or fragmented. The paper also showed that pellets containing microplastics can be
transferred to larger organisms, C. typicus pellets were shown to be transferred to the larger copepod C. helgolandicus via coprophagy,
emphasising the issues previously discussed.
Zooplankton pellets are an important source of food for a
wide variety of marine organisms globally, this highlights that the problem is
not confined to a few species but can have serious wider impacts on
communities. I would be interested to understand more about the different types
of plastics impacting on faceal pellets, as this study used polystyrene which
is used for most packaging eg plastic cutlery, yoghurt pots etc. However,
polyethylene (plastic bags, single-use plastic bottles etc) is manufactured in
a variety of denisities so different plastics may have differing effects.
Paper reviewed:
Cole, M., Lindeque, P. K.,
Fileman, E., Clark, J., Lewis, C., Halsband, C., & Galloway, T. S. (2016).
Microplastics alter the properties and sinking rates of zooplankton faecal
pellets. Environmental science
& technology, 50(6),
3239-3246. http://pubs.acs.org/doi/abs/10.1021/acs.est.5b05905
Hey Ellie,
ReplyDeleteYou've found a really interesting paper here. It's sad that they have had to adjust the representative amount of micro-plastics since the publishing of previous papers, just shows how negative our impact really is.
It would be cool if they could trace the plastics through the food-chain, to get a whole picture of the effects that they have on an entire trophic system. It's possibly similar to the accumulation of toxins, like DA in mammals; as the toxin usually enters the food chain at a very low level such as this, and consequently these micro-plastics could accumulate in larger organisms and cause serious damage. I am aware that plastics are a huge issue for large vertebrates, such as sea birds, but I haven't read or seen much about the accumulative damage of micro-plastics within the top consumers? However, this would probably take a lot of work, so maybe it's not achievable yet.
Also, I agree with you that this is a really great paper, but it would be even better if they could follow it up with different types of plastics.
Thanks for the post,
Harriet
Hi Harriet,
DeleteThanks for your comment, yes I agree sadly not much work has been done on the accumulation of microplastics throughout the food web. As research into microplastics develops hopefully in the future we will see some field studies done, however, like you say, this must be very difficult to perform.
Meanwhile, I have found this paper by Batel et al who say they look into the accumulation of microplastics along the food chain ending with vertebrate model – which has not been done before. Although perhaps not truly representative of the natural processes, it is a good start. They had a very simple food chain of Artemia spp. and Danio rerio (the Zebrafish), D. rerio readily injested Artemia spp. who had previously consumed microplastics, and these could be seen in the intestinal track of the Zebrafish. Although this is not truly representative of a food chain their methodology is a good starting point as the only way I could see to do this would be to allow for the consumption of fluorescent microplastics and then monitor them throughout the food chain, however doing this in the natural environment would be incredibly difficult.
I mean of course, we see evidence all the time of large vertebrates with plastics accumulated in their intestinal system, this year alone we’ve seen around 20 sperm whales washed up in the UK with plastics in their stomachs. It would be very useful to understand how to distinguish between the quantities of microplastic accumulation through the consumption of prey in large vertebrates.
Interesting, if very depressing.
Many thanks,
Ellie
Batel, A., Linti, F., Scherer, M., Erdinger, L., & Braunbeck, T. (2016). The transfer of benzo [a] pyrene from microplastics to Artemia nauplii and further to zebrafish via a trophic food web experiment–CYP1A induction and visual tracking of persistent organic pollutants. Environmental Toxicology and Chemistry. http://onlinelibrary.wiley.com.plymouth.idm.oclc.org/doi/10.1002/etc.3361/epdf
Hi Ellie,
ReplyDeleteThanks for your great review – the more we learn about microplastics the more depressing and fascinating the field simultaneously becomes. There’s a great review (Zettler, et al 2013) on the microbiology of the plastisphere and, giving the prevalence of hydrocarbonoclastic bacteria in the sea and the rapid evolution/plasticity of invertebrate microbiomes, I would be fascinated to see if a selection pressure exists in polluted coastal areas to sequester bacteria of such metabolic capabilities in the intestinal tract of zooplankton. More plastic degradation in the gut would allow more room for natural prey digestion. It would be an intriguing insight into anthropogenically mediated microevolution.
Thanks again,
Davis
Zettler, E. R., Mincer, T. J., & Amaral-Zettler, L. A. (2013). Life in the “plastisphere”: microbial communities on plastic marine debris. Environmental science & technology, 47(13), 7137-7146.
Hi Davis,
DeleteGlad you enjoyed my review. Very interesting point on the degradation inside the intestinal track, if the gut was able to break down these non-natural entities then maybe there would be less of an issue towards the individual and when egested. Perhaps it would be worth looking into the types of plastics, again, as some which possess different densities and properties may be able to be broken down easier. I recently read (I will try to find a paper) about Pseudomonas a strain of bacteria able to break down plastics, which although is not currently well studied it does show potential. The paper I reviewed spoke a little about the microplastics inside the intestinal tracks, discussing that larval with simplistic intestinal tracts have little impact on the individual itself from microplastics, so this would be an interesting point for further research.
Thanks for the paper also, I read it with Johanna’s posts ‘The hitchikers guide to the Oceans’ and ‘The restaurant on the polystyrene microparticle’ which are both very interesting blogs, if you haven’t seen them already, definitely worth a read alongside this. As with the slower sinking rates pointed out in my review and the ability of colonisation by opportunistic pathogens such as vibros from Johanna’s post I take this to mean opportunistic microbes could potentially colonise at higher rates and be transported to across open waters, when aggregates are sinking slower.
Many thanks,
Ellie
Hi Ellie,
ReplyDeleteReally interesting post you have here! I assume that when comparing the sinking rates between microplastic particles and faceal pellet with microplastics, the faceal pellet sinks quicker, resulting in large quantities of microplastics reaching the deep sea environment.
It's funny you should post this because just a few months ago, we discovered deep sea animals that had ingested microfibers for the first time. This included organisms such as hermit crabs, squat lobsters and sea cucumbers, revealing just how bad this our polluting habits have become.
Thanks for the read!
Stefan
Taylor, M., Gwinnett, C., Robinson, L. and Woodall, L. (2016). Plastic microfibre ingestion by deep-sea organisms. Scientific Reports, 6, p.33997.
Haven't got much more to add, just thought you may be interested in the paper.
Hi Stefan,
DeleteI think you may have misunderstood me, (or perhaps I haven’t explained very well!) I think you are saying that the faceal pellets containing microplastics sink faster? This was how I understood the paper for much of my reading too, however after a few attempts at writing the blog, I realised my confusion.
What I believe the paper shows is that the densities in the pellets containing microplastics are much lower than pellets without microplastics (Illustrated in F2b of the paper if you wanted a visual aid!), due to the lower densities, the pellets with microplastics egested by C. hegolondicus sink at a slower rate than those without microplastics (illustrated in F2C - Figure 3 is also very helpful).
But, yes, as far as I can see you are completely right with regards to the issues facing the deeper waters. Seemingly to me, as microplastics are ingested in surface waters they then get repackaged and egested into deeper waters, therefore increasing the levels of microplastics towards the benthos – scary stuff! As this allows organisms that would not normally be affected by microplastics to consume and enter that particular food path. – Exactly like you’ve shown with that paper, thank you for that, looks like an interesting read! – Efforts of cleaning surface waters are coming to light a bit more now, so maybe if surface water microplastics problem can be tackled then less will be transported lower in the water column.
Thank you for your comment and the paper!
Ellie