Source: Jiang, Peilin, et al. “Microplastic-Associated Bacterial Assemblages in the Intertidal Zone of the Yangtze Estuary.” Science of The Total Environment, doi:10.1016/j.scitotenv.2017.12.105.
According to Science, 4-12 million tons of plastic is added to the ocean per year. This is a massive world problem because plastic pollution is dangerous for our marine systems in many ways. For example, it is not biodegradable and remains in the ocean indefinitely. Additionally, small particles that float on the top of the water look like a cheap lunch for the aquatic animals that end up on our plates. Microplastics, plastic particles that are less than 8mm in size, can be especially damaging because they are so easily ingested by animals and can easily carry microbes from one environment to the next
Coastal zones are especially important for plastic pollution studies because they represent a transition between human input and the open ocean. Two of the largest coastal collection sites for marine plastics are estuaries, the aquatic area where a river meets the ocean, and coastal intertidal zones, the area on a beach that is covered by water only at high tide. China is the most populous country in the world, so microplastic pollution in their coastal waters affects large populations of both marine animals and humans.
These coastal habitats are a prime spot for studying how plastic input affects natural microbial populations. The microbes found on the plastics in these habitats can tell us about the plastic pollution in the water and vice versa. There is both good news and bad news when considering how microbes and their microplastic homes affect each other. The bad news is that microplastics are small enough that currents can easily move them, spreading their attached microbes to new environments. The good news, however, is that some bacteria digest the carbon from plastic, or change plastic’s chemical structure, as part of their metabolism. Both of these processes can affect how long the microplastics last in nature, as well as their toxicity.
So, What’s Up with the Microbes?
This study set out to collect microbes from microplastic samples at three intertidal sites in the Yangtze River Estuary in Shanghai, China: Xiangshan Bay, Chongming Island, and Lvsi Port. Their goal was to better understand what plastics types and microbes were at each site. In order to figure out what plastic types each sample contained, they used an instrument that scans samples with infrared light. Then, DNA was removed from the samples and computer programming was used to figure out what microbes were there.
The two sites that were least affected by fresh water input, Xiangshan Bay and Lvsi Port, had similar microbes. Chongming Island, a site in the middle of the estuary, had a unique population of microbes. The pattern of what plastic type was found where did not match the pattern of where the microbes were found. Instead, the microbes were more associated with their environment. This means that microbes may attach to microplastics and move elsewhere, regardless of the type of plastic. Additionally, in every sample, bacteria that can eat plastic or change its chemical makeup were found. All three sites had bacteria that cause fish disease and at Xiangshan Bay, the most urban site, bacteria that cause human diseases in the gut were found.
Putting it all Together
Urban centers have a higher than average influx of plastic to the ocean. Each of these three urban locations in China have different environments that may be affecting microbe or plastic type, for example, Chongming Island has the highest influx of freshwater. Additionally, the discovery of disease-causing bacteria was alarming, as they could be dispersed or ingested by marine creatures and transferred up the food chain, causing issues for fish farming, and human health. Understanding dispersal of plastic types and their associated microbes can help us better understand marine pollution, as well as ways to decrease the negative effects of plastic toxicity and microbes that cause disease.
I am a Master’s Candidate at University of Delaware where I study the evolution of microbes in the sediments where rivers meet the ocean. Organisms in these sediments, Asgard archaea, could be the link between early microbes and the evolution of advanced life: AKA everything you can see with your eyes! Outside of biology, I love to write. I even wrote for a music magazine in my home town for 6 years. Writing for Oceanbites provides an opportunity to combine my passion for science with my zeal for writing. When I’m not in the lab, I am outdoors, whether its running a nature trail, backpacking, or rowing with my team.