“The normal microbial community in deep water is different from that found at the ocean surface — two different worlds almost in a liquid space. The amount of microbes per liter of ocean water in the deep sea is also much lower than that found at the surface,” says Annika Vaksmaa. Thus, a heavy rain of “alien” microbes falling from above in plastic shuttles can disturb the deep-sea community.”
In subtropical eddies, the concentration of floating plastic debris elements is very high. Thus, the amount of microbes on the floating plastic particles is also very high in these areas. The vortices thus provide an excellent natural laboratory for checking whether the sunken plastic particles act as an elevator for microbes. Matthias Egger: “We wanted to test whether plastic particles, once sinking from the sea surface, also transport microbes vertically downward toward the ocean floor.”
Mathias and Annika sampled plastic in the subtropical circulation of the North Pacific (also referred to as the Great Pacific Garbage Patch due to the high loads of floating plastic in these marine waters). They did this by trawling the surface and deep water layers with a fine mesh intertwined. They analyze the collected particles by extracting DNA from biofilms that cover small plastic particles. After sequencing the DNA, they were able to identify the microbial communities that live on each plastic particle.
“In fact, we found that the plastic acts as an elevator in the water column. But the passengers (microbes) enter and leave the elevator very quickly,” says Vaksma. “DNA sequencing showed that microbial communities on floating plastic particles are different from those on deeper water layers.” The researchers concluded that during drowning, microbes apparently detach from the plastic and other microbes, from the surrounding water, and adhere to the empty spaces on the plastic. Vaksmaa: “I was surprised by how clear the results were that the reach of the ‘vertical plastic shuttle’ actually stops a few meters below the surface.”
In addition, the researchers found that a significant portion of the microbes on plastic surfaces were called hydrocarbon decomposers. As the name suggests, these bacteria are known to break down hydrocarbons such as oil and possibly plastic as well. “This isn’t the first time we’ve found hydrocarbon decomposers on plastic,” Vaksma says. “Also in my previous study on plastic colonies in the Mediterranean, I found a lot of these organisms. This raises the question whether these hydrocarbons are actually eating or decomposing the plastic in the ocean.”
This study does not provide a solution to global plastic pollution and the changes it is having on ocean biodiversity. This study was a collaborative project. Vaksmaa: “I am very happy to work with Matthias from The Ocean Cleanup, because such large expeditions to remote sites need great facilities and collaborators. Only together can such excursions be carried out. I know Matthias since we did our Ph.D. in different universities. From What’s important to realize is that in science – this is not the work of a single woman/man, but a team effort.”
This study is part of a larger ERC-funded project led by Helge Niemann at NIOZ that aims to reveal what types of microbes live on plastic and to what extent ocean plastic serves as a food source for microbes. We are investigating the fate of plastic at sea and the power of ocean self-cleaning. That is, we want to know if marine microbes can eventually break down plastic debris and how quickly they can do so,” says Niemann.
Vaksmaa: “We aim to answer the remaining open questions during similar ocean expeditions, next time in the North Atlantic. We cannot currently rule out whether some single organisms remain on the shuttle and enter the depths of the ocean as extraterrestrial beings. There they invade the indigenous communities that It lives in deep water layers. We will try to verify this on future expeditions.”
Marine Pollution Bulletin
Microbial assemblies on microplastics in surface waters differ from groundwater in the subtropical circular North Pacific
The date the article was published
August 4, 2022
Some researchers work for Ocean Cleanup.