Why Putting Shrimp on Treadmills is Good Science

Example for: What Does this Scientific Paper Mean for People?

It’s likely you’ve come to this post after seeing my related post, “What Does this Scientific Paper Mean for People?” If not, I recommend skimming it first, as it details the process I’m about to use to assess the merit of a pretty famous example of potentially wasteful science.

First, I’ll find a few pieces of journalism about the shrimp situation.

 

shrimpscreenshot
Screenshot from the video

The study originally came to media attention when a video was posted to Youtube from David Scholnick’s (one of the researchers) website. One of the early articles on the video and surrounding research was by Sara Goudarzi (it can be found on Live Science and NBC). It’s a short article, without much context. Most of the implications can be found in one paragraph at the bottom of the article.

 

“Shrimp dealing with an infection would be less active and might be limited in their ability to migrate, find food, and avoid being eaten, Scholnick said. “These studies will give us a better idea of how marine animals can perform in their native habitat when faced with increasing pathogens and immunological challenges.””

So here is a bigger biological context: disease can affect parts of the shrimp life cycle. But why should we care? And why is this relevant?

There is a later report by Mike Selizic on Today which makes much more of an effort to detail the broader implications of the study.

“Both climate change and the runoff from agriculture and human activities affect the composition of ocean water, which in turn can lead to higher levels of bacteria. If shrimp with bacterial infections have less endurance and strength, that affects their ability to survive.”

Now we know more about the relevance. Human activity may cause increased disease vectors in shrimp. But still, why should we care about shrimp survival?

“Now that Burnett and Scholnick have a handle on how disease affects shrimp, they’re applying treadmill research to other critters that most of us think about only when they show up on a menu.”

In this case, it’s obvious and assumed as obvious by the article: we eat shrimp! Therefore, we should understand how disease affects them and other creatures we eat.

 

shrimp trawler
Shrimp Trawler

 

My example is so far showing that you can’t just take one journalistic article as your entire reference for the relevance of a study. That is especially true in this case. Many later articles focused on this study as a waste of taxpayer dollars and fruitless government spending. In cases like this, where the journalism is obviously controversial or political, it’s time to look to the paper itself. I’ve selected one paper that was within the larger study the treadmill video was a part of and conducted by the same team of researchers (David Scholnick, Karen Burnett, and Louis Burnett): Impact of Exposure to Bacteria on Metabolism in the Penaeid Shrimp Litopenaeus vannamei.

First, I’ll examine the Introduction. This is a relatively short paper; the Intro jumps straight into a very specific line of research, discussing first the role of gills in the crustacean immune system (the gills may eject bacteria). Large levels of bacteria may also impede respiratory performance in crustaceans. One statement relates to a somewhat larger picture:

“…low levels of environmental oxygen can impair the rate at which bacteria are cleared from the hemolymph.”

Although the Intro doesn’t go into more detail than this. It concludes with the specific research question: the investigators want to test respiratory performance of shrimp that have been exposed to bacterial pathogens in water with normal and low levels of oxygen.

The Discussion may have some larger context as well. The researchers noticed a significant “metabolic depression” in the infected shrimp, at levels that surprised even them and are worth of further research based on discrepancies between their test and other related tests. The Discussion then reiterates how bacterial infection and low-oxygen environments may compound each other’s effects on shrimp respiration and metabolism, an observation supported by their experiment.

Based on levels of lactate produced by the infected shrimp (lactate being the byproduct of anaerobic respiration, which takes over when there isn’t enough oxygen to support the muscular system), the researchers estimated there to be a “29% reduction in overall metabolism” because of bacterial infection. This is a big number, but what does it mean?

The last statement in the paper is perhaps the broadest and most meaningful.

“Our results provide a plausible explanation for the increased susceptibility of crustaceans to infectious disease in hypoxic environments and lend support for further investigations to determine how reduced ATP production associated with exposure to bacteria may impact overall activity and performance.”

Crustaceans respond worse to infection in low-oxygen environments. Though it isn’t stated outright why we should care about their “activity and performance,” it seems fairly obvious that it is because crustaceans are important to human dietary intake. We eat shrimp in large quantities, so it matters how they perform as a species (as in, if they can survive easily).

However, there’s one statement that the researchers could’ve gone into more that would’ve related things to a bigger picture. They keep mentioning hypoxic environments, but why would this be timely? This will require some further investigation.

The paper is somewhat short, and shorter papers are often so either because of space requirements (they can’t afford to give a lot of words over to explaining background and context) or because the background and context are assumed based on the expected readers of the paper. In this case, I’d go with the latter, at least partially. As someone with a background in marine science, I can already tell you why considering hypoxic environments and their effects on food animals like shrimp is important and relevant.

To delve more into hypoxia, I followed some citations. Boyd and Burnett’s Reactive Oxygen Intermediate Production by Oyster Hemocytes Exposed to Hypoxia led to a few more papers on hypoxic environments in general which mentioned how they are often seasonal, can cover large areas, and can have large effects on organisms living there and are associated with mortality events.

algae
Algae blooms like this one can soak up oxygen

Simply googling hypoxia at this point would easily lead to a more obvious relevance to humans: our actions, specifically the overproduction of certain nutrients mostly due to agriculture and industry, are fueling algal blooms in estuaries and gulfs. When the algae die and start to decay, the process consumes oxygen in the water and leads to a hypoxic event. Therefore, we are directly causing a drastic change in certain environments—understanding that change on different levels is in our best interest.

 

More information can be found in the other methods I mentioned at the end of my original post. To expand our viewpoints, we can find opinion pieces about the study. Betsy Hammond wrote a piece for The Oregonian allowing David Scholnick, the researcher who originally posted the shrimp treadmill video, to defend his work. There is one paragraph which sums up the defense pretty well:

“His decision to put shrimp on treadmills was a very tiny part of a much larger study by two College of Charleston professors, looking at how shrimps’ immune systems react when ocean warming or pollution makes it hard for them to breathe. The National Science Foundation paid $426,000 for that study, which was designed to help promote food safety and the health of commercial shrimp fisheries.”

So there’s an obvious meaningfulness to the work. Scholnick even published his own post about the entire incident; it’s a good way to get everything from his viewpoint and really see how everything played out.

There’s one last avenue of investigation we can follow, here. The NSF grant information for the larger study that the paper and video were a part of is available to view online. The entire Abstract for the project is one long justification for its existence: detailing the rise of hypoxic conditions, commercially important crustacean populations that may live in vulnerable environments, and what environmental and physiological variables may react to low oxygen conditions. It is very clear that more research into specific, physiological-level effects are needed to understand effects on entire populations of crustaceans.

So what have we learned from all this?

First, sometimes it takes a lot of research to figure out the big picture context of a single scientific study.

Second, good journalism is important in relating between science and society when the links are not obvious or too broad in scope to be in the original paper.

Third, putting shrimp on a treadmill was worthy science.

 

To the reader: are there any scientific studies that you’ve had difficulty relating to larger contexts, or that you can see the relevance of but others seem not to be able to? Also, I can repeat this procedure for papers you give me if you want more examples! Feel free to make requests.

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