In today’s society, the demand for plastic is largely driven by its convenience and practicality. However, as global plastics production approaches 400 million tons each year, the benefits of this man-made material are largely outweighed by its environmental consequences. Since as early as the 1970’s, researchers have studied the impacts of plastic debris on marine life at both population and ecosystem levels (UNEP, 2016). Keep in mind that at this time only around 50 million tons of plastic were produced annually (Guern, 2019). Now, as that number has exponentially increased by almost four times, you can expect that the oceanic ramifications have skyrocketed at well.
In 2015, a study conducted by a team at the National Center for Ecological Analysis and Synthesis reported that about 8 million tons of plastic end up in the ocean each year. Consequently, because these waste materials are designed to be long lasting and not readily broken down, this number builds up allowing plastics to pollute marine ecosystems indefinitely. Only around 20 percent of this debris comes from plastics being directly disposed of into the ocean. The majority of plastic, the other 80 percent, is brought into the ocean due to improper waste disposal and the movement of light plastics through wind and rain (Guern, 2019).
The extent to which marine debris invades the ocean is much greater than what most people see. While coastlines are often littered with various plastics, most of what goes into the ocean circulates in gyres creating highly concentrated stretches of garbage that travel with the currents. Aside from plastic buildup, the movement of these materials through ocean circulation also presents an opportunity for the spread of pathogens and other invasive organisms. The idea that species could be transferred by rafting on plastic was solidified after 289 Japanese marine species were found living on debris washed ashore in North America (Therriault et al. 2018). For obvious reasons, the introduction of non-native species to an area could potentially have major impacts on marine ecosystems. Not only does this affect marine life but the spread of certain bacteria has also been shown to have negative consequences on the health of humans (Snoussi et al. 2008).
According to the Food and Agriculture Organization of the United Nations (Globefish, 2020), “ghost nets”, a term referring to fishing nets that have been lost or abandoned, are estimated to make up around 10 percent of ocean plastic. Fishing nets are one of the main factors driving entanglement as they are literally designed to trap and capture fish. However, when set loose with no regulation, they can affect many more animals than just fish. Any oxygen breathing marine animals such as whales, seals, turtles, and birds present high risk of death from entanglement. Items like plastic rings, bags, nets, rope, and many more can get caught on these animals leading to immediate suffocation or an impaired chance of survival by creating drag which increases energy expenditure and may overall lead to starvation. The International Whaling Commission estimates that worldwide entanglement kills 300,000 cetaceans each year (NOAA Fisheries, 2020). This number is much greater for smaller animals such as sea turtles that are less likely able to disentangle themselves.
A less visible impact of plastic pollution is ingestion. Plastic may end up in the stomachs of animals for a few reasons, the most common being that they mistake the plastic for food. The consequences of this, however, vary between species as some are easily able to expel the plastic while others are not. Toothed whales and turtles, for example, have a very hard time eliminating plastic once it is ingested. As a result, the plastic remains in their stomach, decreasing the amount of food that can be taken in at a time. If choking is not the immediate outcome, these animals may die from starvation as space in the stomach becomes limited. More recent studies have focused on the role of microplastics in marine environments and what impacts they might have on the food web. Microplastics are plastic particles that are 5mm in length or smaller and can be found in abundance throughout the ocean. Studies have found that even the smallest marine organisms, zooplankton, are able to ingest these particles and pass them up the food chain due to the fact that they cannot be digested. Additionally, filter feeders, like whales and sharks, take in gulps of water at a time, trap food, and expel the remaining sea water. Unfortunately, these microplastics remain with the food and accumulate in these animals’ stomachs. With this, the concern arises in the fact that microplastics are often contaminated with toxic chemicals that have shown to negatively affect the reproduction and survival in many animals (Chatterjee et al. 2019).
The scary reality is that the impacts on marine environments will continue getting worse until plastic consumption significantly declines. Study reviews note that plastic ingestion or entanglement has affected all known sea turtle species and more than half of all marine mammal and sea bird species (Gall et al. 2015). Methods for removing ocean plastic pose challenges due to both the high volume and spread of waste throughout the globe. This paper provides a brief summary of the different impacts that plastic debris has on marine animals, however, advanced studies continue to draw on new information regarding the susceptibility of different species and environments to negative impacts.
UNEP (2016). Marine plastic debris and microplastics – Global lessons and research to inspire action and guide policy change. United Nations Environment Programme, Nairobi.
Guern, C.L. (2019) “When the Mermaids Cry: The Great Plastic Tide.” Coastal Care. https://plastic-pollution.org
Therriault, T. W., J. C. Nelson, J. T. Carlton, L. Liggan, M. Otani, H. Kawai, D. Scriven, G. M. Ruiz, and C. C. Murray (2018) “The invasion risk of species associated with Japanese Tsunami Marine Debris in Pacific North America and Hawaii.” Marine Pollution Bulletin 132:82–89
Snoussi, M., E. Noumi, D. Usai, L. A. Sechi, S. Zanetti and A. Bakhrouf (2008). “Distribution of some virulence related-properties of Vibrio alginolyticus strains isolated from Mediterranean seawater (Bay of Khenis, Tunisia): investigation of eight Vibrio cholerae virulence genes.” World Journal of Microbiology and Biotechnology 24(10): 2133-2141
GLOBEFISH – Information and Analysis on World Fish Trade (2020). “Innovative Efforts Tackle Ghost Fishing Nets and Bring Value to Waste.” http://www.fao.org/in-action/globefish/fishery-information/resource-detail/en/c/388082/
NOAA Fisheries (2020). “West Coast Large Whale Entanglement Response Program.” West Coast Regional Office
Chatterjee, S., Sharma, S. (2019) “Microplastics in Our Oceans and Marine Health.” Field Actions Science Reports [Online], Special Issue 19 URL : http://journals.openedition.org/factsreports/5257
Gall, S.C., Thompson, R.C (2015). “The Impact of Debris on Marine Life.” Marine Pollution Bulletin 92 (2015) 170-179 http://dx.doi.org/10.1016/j.marpolbul.2014.12.041
Research review paper written by summer intern, Julia B. Julia is a student at the University of Wisconsin studying Biology.