Book Review

Plastic Problems in Marine Pathways

What if I told you that the organisms in the ocean produce half of the oxygen we breathe? Then what if I told you that plastic in the ocean can affect these organisms and other parts of the environment? Pretty crazy right? Read on to learn more about how small plastics in the ocean can have such intense consequences.

Citation: Shen, M., Ye, S., Zeng, G., Zhang, Y., Xing, L., Tang, W., Wen, X., Liu, S., 2020. Can microplastics pose a threat to ocean carbon sequestration? Marine Pollution Bulletin 150, 110712. 

An age of convenience

Everywhere we look, plastic surrounds us. Whether we’re in a grocery store, out to eat or simply brushing our teeth, the convenience that plastic brings to our lives has made most of us extremely reliant on these disposable items.  However, plastic items have a way of making their way into the oceans where they harm wildlife and disrupt the environment. The impacts of these larger items are often well-known, such as the extent of the Great Pacific Garbage Patch or the impact of plastics on Albatrosses. Over time larger plastic objects break down into tiny pieces called ‘microplastics’ that are just as bad for our oceans. These microscopic pieces can stop the most important processes in the ocean from happening.

The plastics problem represented by a fish made of plastic bottles about to eat a turtle. Image: Getty Images

The microplastic problem

Our oceans are a sink for carbon dioxide. This means that they absorb the excess carbon dioxide produced by human activity (eg. transportation, agriculture, etc) and help maintain Earth’s balance. There are different pathways in which carbon can become absorbed by the oceans, and unfortunately, microplastics have been shown to affect all of these pathways. A recent study describes the ways in which microplastics can prevent the oceans from absorbing carbon dioxide:

1) Block sunlight from phytoplankton. Since microplastics tend to sit on the surface of the ocean for long periods of time, their accumulation can prevent tiny organisms called phytoplankton from getting enough sunlight. These cells need sunlight to carry out photosynthesis (the process by which they take in sunlight), convert carbon dioxide into organic carbon (sugars) and produce oxygen as a byproduct.  If microplastics prevent the ability of phytoplankton to take in carbon dioxide, the entire marine food web will be affected.

Plastics come in all shapes and sizes – but all affect our ocean. This is a water droplet of microplastic beads on a finger for size reference. Image credit: Woods Hole Oceanographic Institution

2) Lead to toxic effects on zooplankton. Zooplankton are the ‘second link’ to the marine food web–they eat phytoplankton and then get eaten by small fish. Zooplankton are important for transferring carbon to higher levels of the food web. This particular study examined copepods,  a type of zooplankton. These copepods reduce their natural food intake (phytoplankton) by 40% after plastic ingestion. If they don’t get enough nutritious food, they don’t have enough energy and as a result, their eggs are smaller and less likely to hatch.

3) Interrupt carbon sinking to seafloor. Zooplankton produce fecal pellets which are important for recycling energy within the ocean’s surface because they are broken down by bacteria. These fecal pellets also sink to the seafloor and take carbon with them to the bottom of the ocean. Fecal pellets can be full of microplastics and sink at almost one a half times slower than a fecal pellet without plastic. This means that carbon is taking longer to get to the seafloor, so less carbon is likely to be ‘stored away’ in seafloor sediments. In addition, microplastics themselves can sink out to the seafloor and affect carbon cycling by interrupting seafloor organisms’ ability to take in sinking carbon and sequester it into the sediments.

Screenshot of a video showing research by lead author Alina Wieczorek (NUI Galway). Microplastics are depicted as small pink and green dots in upper layer of the ocean. Check out the video here.

There are many pathways in the ocean that can be affected by the high concentration of microplastics. We need to further study how microplastics directly affect the rates of these pathways; however, we know that we should start now to change our actions for the future.

‘Mr. Trash wheel’ invented by John Kellet is seen above in Baltimore Harbor cleaning up trash. Since its installation in May 2014, the solar powered trash wheel has picked up over a million pounds of trash. Image credit: The Waterfront Partnership

Optimism for the future

Although humans have become inherently reliant on plastic materials, there is a huge movement towards a “zero-waste” lifestyle that anyone can start moving towards. This zero-waste lifestyle involves using plastic-free everyday items such as shampoo bars, bamboo toothbrushes and wooden utensils you can carry with you and conveniently pull out the next time you reach for a plastic fork! If we can collectively change our mentality to focus on reducing plastic use, re-using items instead of relying on the convenience of plastics and developing technology to clean up our mess, we may be able to solve the plastic problem.  And last but not least, don’t forget that even just one person can make a difference and inspire the people they care about towards action!

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