• Tamsin

A Sea of Plastic

Updated: Aug 4

This week, we're honoured to have Valérie Cornet share her expertise in marine biology. As a PADI Divemaster and underwater photographer, Valérie always had one foot in the water. She decided to pursue her passion at James Cook University, Australia, where she is currently finishing her postgraduate studies. In this piece, Valérie explores the disastrous consequences of plastic pollution on marine ecosystems and human health, and invites us to rethink our global economy in order to preserve one of the most biodiverse habitats on Earth.

" When talking about the effect of plastic pollution on marine ecosystems, the first thought that pops into our heads tends to be one of a dead turtle killed by plastic straws that have strayed into our ocean. It is a very striking image and one that requires attention. However, this just touches the tip of the iceberg, where the iceberg is the plastic pollution problem in question. 

It is expected that by 2050, the plastic in our oceans will outweigh the fish, a truly terrifying and heartbreaking thought. It is estimated that over 700 marine species are currently threatened by marine plastics. This number is expected to rise due the staggering 9.5 million tonnes of plastic being introduced into the ocean every year. These include not only large plastic waste, such as plastic bags, bottles and other debris, but also microplastics and nanoparticles, which are plastic particles that are smaller than 5mm or 100nm, respectively. Introduced into our oceans primarily through land-based activities such as run-off, illegal dumping, beach visitor waste and inadequate waste management, single-use plastics have found their way into all corners of our planet, being found in all marine ecosystems, from the depths of the Mariana trench to the open oceans and our highly biodiverse coral reefs. 

So how does plastic actually affect our marine ecosystems?

Macroplastics affect our marine animals through direct effects by ingestion, entanglement and lacerations. Ingesting marine plastics has seen detrimental effects throughout all trophic levels (food chain levels), from causing starvation in large marine mammals such as whales and dolphins, as well as filter feeders, such as manta rays, to plankton. Fish have been found to develop fewer and less healthy offspring when presented with a plastic-contaminated diet. On top of this, macroplastics have a tendency of getting entangled with larger fish, mammals and corals, as well as having internal effects, perforating organs and clog digestive tracts to inhibit further ingestion of food that is needed by these animals. The lacerations that they may cause have been linked to an increase in susceptibility to disease and viral attacks. Specifically for corals, studies have found that for a branching coral that has come into contact with plastic waste, the likelihood of disease contraction increases from 4% to 89%, a shocking difference. Large plastic debris may also block corals from the sunlight they need for survival. This, along with the current pressures on these ecosystems from rising sea temperatures, ocean acidification, habitat destruction and overfishing, poses an additional issue, synergistically threatening our marine ecosystems. 

Microplastics, on the other hand, present a different, more “invisible” kind of problem. As these particles are inconspicuous to the human eye, it is easy to disregard the severity of their prevalence in our oceans. Ingestion of these microplastics has led to similar effects of its macro counterpart, being linked to reproductive and developmental complications in various species of plankton and fish, especially copepods. This has been seen to have unpredictable effects on these planktonic populations, leading to both booms and busts in numbers, which in turn have influenced population numbers of predatory populations that feed on plankton. Being at the bottom of the food chain, this can have disastrous effects on ecosystem dynamics, potentially skewing the ecosystem structure and pushing species of a higher trophic level to go extinct. A recent discovery also found that worryingly, corals have been found to preferentially feed on microplastics over their natural particulate food, accelerating the process of bleaching and eventually death. Microplastics not only have water-based effects, but also land-based, having been linked to influencing sand’s surface temperature, which may further lead to shifting sex determination of turtles and throwing off the balance of sexes in populations, depleting populations.

These direct effects on animals, both large and small should already be enough to scare us away from using single use plastics. Yes, we all want to save the whales and turtles, but this problem is made exponentially worse by affecting the microscopic beings that allow for ocean dynamics to run smoothly. By disrupting plankton populations, the flow of carbon and nutrients will be altered, having unknown effects on all ecosystems, making it virtually impossible to prepare for and mitigate these changes. To make matters worse, the mere presence of plastic on the sea surface was found to worsen climate change directly. Where sunlight accelerated the breakdown of plastic and during the breakdown process, methane, a greenhouse gas was released into the atmosphere. The presence of microplastics in Arctic waters also disrupts the formation and melting processes of the ice caps, further aggravating sea surface temperature rises. The list of harmful effects presented by marine plastics just never ends. 

Still not convinced? Plastics do not only detriment marine animals and its habitats, but they come back to harm us, humans. Not only has plastic particles been found in fish, but also in everyday staples such as salt, sugar, shellfish, honey and even bottled water. We therefore cannot help but ingest plastic, even the vegetarians out there! Ingested plastic is directly introduced into the hormone system, having been linked to increased risk of cancer, reproductive difficulties, behavioural disorders and various other human disorders. 

So what is being done and what should we do?

With marine ecosystems being some of the most vulnerable, yet biodiverse on our planet, it is important that change occurs now. This is a global problem and therefore requires international attention. Currently, efforts have been shown by organisations like the UN and developed countries such as Norway and Sweden that have implemented robust waste-management systems and continue to further research regarding the effects of plastic pollution and the efficiency of waste management. Nations and companies around the world have started shifting towards banning single use plastics, but without a more dramatic modulation of our use of plastics, its continuing effects on marine ecosystems may be irreversible. 

This is an ecosystem that can be compared to a ticking time bomb and without dramatic action, the cumulative effects it faces may destroy some of the most beautiful habitats we have on Earth and the animals that call them home. Because of this, there is a need to advance education and innovation, in order to better understand the effects of plastic pollution and pave the way for better action to mitigate its effects and hopefully turn to a greener future. This begins with individuals being mindful at a local scale, but extends to national and international scales, where corporations and countries need to work in unison to stray from the use of landfills and single use plastics. With this monstrous problem we face, it is hard to ignore the detrimental effects of marine plastic pollution, as it not only affects all corners of our planet, but also us humans, directly. Turning our heads away from this problem should therefore be tackled first hand and treated as a primary threat to humanity."

By Valérie Cornet

Follow her work @valgoesdeep


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. Environmental science & technology, 49(2), 1130-1137.

Duncan, E. M., Arrowsmith, J., Bain, C., Broderick, A. C., Lee, J., Metcalfe, K., ... & Godley, B. J. (2018). The true depth of the Mediterranean plastic problem: Extreme microplastic pollution on marine turtle nesting beaches in Cyprus. Marine pollution bulletin, 136, 334-340.

Jamieson, A. J., Brooks, L. S. R., Reid, W. D., Piertney, S. B., Narayanaswamy, B. E., & Linley, T. D. (2019). Microplastics and synthetic particles ingested by deep-sea amphipods in six of the deepest marine ecosystems on Earth. Royal Society open science, 6(2), 180667.

Milios, L., Esmailzadeh Davani, A., & Yu, Y. (2018). Sustainability impact assessment of increased plastic recycling and future pathways of plastic waste management in Sweden. Recycling, 3(3), 33.

Peeken, I., Primpke, S., Beyer, B., Gütermann, J., Katlein, C., Krumpen, T., ... & Gerdts, G. (2018). Arctic sea ice is an important temporal sink and means of transport for microplastic. Nature communications, 9(1), 1-12.

Seltenrich, N. (2015). New link in the food chain? Marine plastic pollution and seafood safety. Environmental Health Perspectives, 123(2), 34-41.

Villarrubia-Gómez, P., Cornell, S. E., & Fabres, J. (2018). Marine plastic pollution as a planetary boundary threat–The drifting piece in the sustainability puzzle. Marine Policy, 96, 213-220.

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