Interview of Rachel Cable

© N.Pansiot/Tara Expéditions

” I have to process the data now.”

Partner of Tara Méditerranée, the lab of Melissa Duhaime in Michigan, participates in the scientific stations. For 10 days, Rachel Cable, American scientist, participated in the sampling on Tara’s rear deck.  Back home, she uses the same protocols in the Laurentian Great Lakes. She kindly answered a few questions about her job on board.


Could you please explain us the purpose of your work?

I work in the lab of Melissa Duhaime at the University of Michigan and we study microplastics, mostly in the Great Lakes right now. We go out on the lakes and sample the surface and subsurface of the water with the manta and bongo nets, just as we do aboard Tara in the Mediterranean. We collect the plastic pieces from those samples and then quantify how many pieces there are in different locations throughout the lakes. We are also trying to find out what microbial communities are growing on the plastics. We use the same protocol that we use on Tara, where we save all of the pieces from each manta tow and keep a few in a solution that will allow us to examine the microbial community in the lab.

I am a research technician in the Duhaime Lab, which means that I am the person in the field doing most of the sampling and then when we go back to the lab, I’m the one who pulls the plastic pieces from each sample and organizes the pieces by size. Eventually, I will aid in the DNA sequencing to identify the species found on the plastics, as well. I also have a great team of undergraduate students at the University of Michigan that help me in my fieldwork and lab work.


How many samples did you get for Michigan during this leg?

We did 5 stations for Michigan, 4 with the manta net and one with the bongo net. I am also here to run an additional experiment in which I can measure the amount of oxygen consumed or created by what is growing on each piece of plastic. We are looking at the oxygen consumption by microbes on the plastics to see the function of the microbial community: is the community photosynthesizing?

We want to know the overall function of the microbial community that is either directly attached to the plastic or attached to the other microbes on the plastic. We are already analyzing the plastic pieces for microbial DNA so we can identify which specific microbes are present, and now we can see what those microbes are doing with the oxygen consumption experiment. If there is a net loss of oxygen on a piece of plastic, there are organisms that are respiring and perhaps using or changing the plastic somehow. If the community is producing oxygen, maybe it is a photosynthesizing community altogether, and the microbes are attached just because the plastic is floating at the top of the water and they can get closer to the light. So that’s the experiment that I did here. I did 6 runs of this experiment with 15 pieces of plastics in each run which were picked from the manta trawl. I have to process the data now.

It seems that the microbeads are also a problem for the Great Lakes region. Could you  explain this?

It’s actually becoming a more popular subject in the US, because we have products that have tiny plastic pieces in them, the kind for cleaning your face, your teeth, etc. Most wastewater treatment plants in the US can’t filter them out, they’re too small. So that goes into the river, the river goes into the Great Lakes (in the Midwest and Canada: Michigan, Illinois, Indiana, Wisconsin, Ohio, Pennsylvania, Minnesota and New York all touch the Great Lakes). The plastic accumulates in the lakes, so you see a lot of plastics but we don’t know how long they stay there. In the Mediterranean the water stays there for a very long time, so plastics stay for a very long time and we observe lots of things growing on them. In the Great Lakes we don’t really see as much, ( ) and they don’t get broken down as much. You see a lot of plastic bottles or tiny bits, but not as many in-between sizes as in the Mediterranean.

There is one paper that has been published on microplastics in the Great Lakes. In Lake Erie, at the end of chain of lakes, I think they were calculating 5000 to 10 000 pieces of plastics in a square kilometer. It is a lot of pieces in one lake!

Are you worried about the microplastics issue?

Yes, we don’t know the impact of plastics in the water, like on animals that eat the plastic, and then we eat those animals, so it is very worrying, but I also think it’s very interesting and I like working on it because it’s a subject we can do something about. For example, in the Midwest, in Illinois, they just passed a law saying that companies can’t produce microbeads for personal care products anymore, so it’s becoming a political issue where people are taking a stand: they want to change what is being put into the water. I think it’s good to study this subject now, and that this is something that can change. It’s not like climate change where it’s definitely on a path that we can’t stop. We can try to slow it down, but we have started something that will continue. I think for plastics in particular, just informing people about this issue can make a huge difference, and I like that.


Interview by Noëlie Pansiot

Related items :

- Scientific goals of the Tara Méditerranée expedition.

- Oceans and plastic.

- Environment and plastic.