What are microplastics ?
Even if today, we are aware of marine pollution, people imagine that plastic bags are the most common type of waste thrown in the ocean. Whereas in fact, this type of plastic – named “macro waste” – represents 10% of the plastic wastes. Most are microplastics, invisible to the naked eye, and not well-known yet. However, scientists already know the negative effects it can have on biodiversity and human population. Indeed, even if we can’t see it, 250 000 tons of microplastic swim in the ocean. Every year, we emit almost 10 million tons, the equivalent of a garbage truck per minute. Through erosion of tires on asphalt or washing of synthetic fiber clothing, either by the degradation of plastic waste, the Organisation for Economic Co-operation and Development (OECD) forecasts the figure to triple by 2060.
What impact ?
Scientists who have looked into microplastic research have determined that marine biodiversity is strongly impacted. Microplastics have an effect on animal diet and reproduction behaviour and could, by the end, even affect humans.
Focus on case studies : microplastics impact on oysters and fish (anchovies)
The French Institute for Ocean Science (IFremer), an institute in charge of marine studies and conservation, has developed a program involving oysters because they are of major ecological interest : it’s an entire ecosystem which is home to great biodiversity and is sensitive to pollution.
Two major impacts of microplastic have been recorded : firstly, microplastics have a chemical effect because wastes expel toxic molecules ; which cause endocrine disruption on oysters (reproduction troubles). Secondly, this microplastic pollution has several physical impacts : plastic replaces food in the animal's diet. It leads to “false satiation”, even starvation, again causing fertility troubles, but also development (growth and immune defenses) which weakens them. We can see the impact notably on the quality of pearls in oysters, which have been deteriorating.
Concerning fish, observations are similar :
Microplastics have significant repercussions on their behaviour, diet and growth. It represents between minus 20 to 35% depending on the species. For the reproduction system, the figure reaches as low as -50%. This data is even more verified for females. It also has an impact on their social and psychological behaviour by increasing their stress level. The University of California has noticed that the majority of marine ecosystems already contaminated with microplastics (93% of marine birds were found to contain microplastics according to IFremer) and one reason is that plastic could have an attractive flavor for marine animals, in particular anchovies which are at the heart of the food chain.
Smell is a vital sense, fish can use it in behavioral contexts such as mating, choosing where to live, migrating and foraging. For their experiment, university scientists studied anchovies' feeding behaviour : when they smell krill (tiny pelagic crustacean which look like a shrimp) the fish disorganize their school and rush for food. In fact, they are acting the same way when they smell microplastic which is, in addition, proportionally the same size.
What’s next ?
Even if plastic is harmful, marine biodiversity tries to adapt and animals develop new behaviours. An example of this is the case of the hermit crab - a little crab with a fragile abdomen ; it occupies empty scavenged gastropod shells to protect it -, highlighted by Polish researchers following the upload of several pictures online. In these pictures, we see the crustacean wearing a bottlecap as a shell.
While usually hermit crabs search for the most solid and camouflaged house, scientists have determined that again, because of the plastic smell, this marine creature completely changes its behaviour. This leads to many troubles, as chemical rejects, high visibility for predators and loss of durability.
Microplastic represents a threat all the more as new forms of life are discovered : German biologists Gunnar Gerdts and Lars Gutow, studying plastic in the ocean, have highlighted a multitude of organisms such as marine woodlice, crustacean larvae and algae that develop in waste residues. Even if for instance, most of the life forms discovered are harmless, some others could become really dangerous. For example, cholera vibrios – bacteria responsible for cholera – which multiply very quickly when the water temperature increases have been recorded on plastic waste.
Other bad impacts are registered now in our metabolism. Because microplastic stays in the fish body, then when we eat it, we eat microplastic too. This phenomenon leads to the same result as for fish, in particular for women. Indeed, for biological reasons, women's bodies have a higher proportion of body fat which constitutes a reservoir for bioaccumulative chemicals, which can leak from microplastics into our bodies.
Nowadays, many biologists, skippers and NOGs try to raise awareness more and more about this subject which is, according to scientists, human responsibility. The best response is not to filter the sea, but to change our behavior.
CuriOcean led studies concerning marine litter in Salthill (Co.Galway). The aim of this study was to analyze the perception of litter in Salthill and its impact on the environment during high peak season, gather behavioural insights and develop temporary, innovative and sustainable litter management solutions for implementation in collaboration with the public. We are now developing a workshop for children to help them become aware of the positive impact they can have on their environment and make them adopt good behavior.
Sources and credits :
Definition of the subject : https://www.zerowastefrance.org/microplastiques-ennemis-invisibles-mais-dangereux/
Impact of microplastic on oysters : https://www.ifremer.fr/fr/microplastiques-et-nanoplastiques-quels-impacts-sur-la-vie-marine
Impact of microplastic on fish : https://www.inrae.fr/sites/default/files/pdf/CP_Toxicite-microplastiques-poissons.pdf
Hermit crab and microplastic : https://theconversation.com/les-bernard-lermite-demenagent-dans-des-dechets-plastiques-et-intriguent-les-scientifiques-223572
Fish feeding behaviour : https://theconversation.com/quand-les-anchois-confondent-le-plastique-avec-un-bon-repas-84081
Head Picture : © Andrea Westmoreland
Picture 1 : © iStock/Svetlozar Hristov
Picture 2 and 3 : © Lambert / CNRS
Picture 4 : © Matthew Savoca
Picture 5 : © Metamorworks / Shutterstuck by The Conversation
Picture 6 : © Bertrand Godfroid / Shutterstuck by The Conversation