Computational Hubris

Guest Essay by Kip Hansen – 25 October 2020

What is pictured in this little image?  And what can it possibly mean?

These are very good questions and should be asked whenever the lede of a science news story is based on an image. 

Why?  “A picture is worth a thousand words”   – – – or so they say.   If that is true, then pictures can also fool us a thousand times more easily than mere words. 

Now, a picture of a new species, say a confirmed photograph of Bigfoot or the Loch Ness monster, might be appropriate for the news.   But I am always skeptical when a science news article is based on an interesting picture, purporting to tell us something important.

The example I am using for today’s essay is related to my recent essay titled: Where Do the Plastic Bottles Go?In that essay, I reported that pelagic plastic (plastic floating in the oceans), exposed to the sun and the waves, breaks down into smaller and smaller pieces which in turn are literally eaten by microbes – such as bacteria.   In other essays on plastic in the oceans, I have asserted that “the natural system finds a way to use most everything – in the case of oceanic plastics, as homes and food.”

After Where Do the Plastic Bottles Go? was published,  our very own CTM sent me a link to this paper:

“Microbial carrying capacity and carbon biomass of plastic marine debris” by  Shiye Zhao, Erik R. Zettler, Linda A. Amaral-Zettler and Tracy J. Mincer.   The full text version is, unfortunately, pay-walled, but a EurekaAlert! story gives us the image used above and a good summary.

“Trillions of plastic debris fragments are afloat at sea, creating the “perfect storm” for microbial colonization. Introduced more than 50 years ago, plastic substrates are a novel microbial habitat in the world’s oceans. This “plastisphere” consists of a complex community comprised of bacterial, archaeal, and eukaryotic microorganisms and microscopic animals.”

What does that mean when we get up in he morning?  It means that sea creatures of all types – tiny, mostly microscopic, little plants and animals – start living on the surface of these bits of plastic that are floating around in the ocean.  The bits become floating homes for these creatures and plants – they live on the surfaces of the bits in what are called “biofilms”.

The new and original part of this study is that “Using confocal laser scanning microscopy with sophisticated imaging software, researchers directly obtained data ranging from cell counts, size and the characterization of microbial morphotypes to complete three-dimensional constructs.”  It is the laser scanning microscope that produced the following image:

As I note below the image, I have adjusted the contract and color levels to enhance this image – the original is rather dark.  It is from photos like these that the researchers have counted the little critters living on the surface of this bit of plastic and formed an idea of how many of what kinds of them are present. 

Why have they done this?   They think that biofilms forming on the itty bits of plastic found in the world’s oceans are a threat: 

“As an unnatural addition to sea surface waters, the large quantity of cells and biomass carried by plastic debris has the potential to impact biodiversity, autochthonous ecological functions, and biogeochemical cycles within the ocean.”

In other words, the plastic bits, found in the top layers of the oceans, supply a happy home for lots of microscopic “bacterial, archaeal, and eukaryotic microorganisms and microscopic animals” – a home that didn’t exist (as far as the researchers know) before the availability of all those little pieces of plastic.   Their worry is that all that “extra” life will use up the resources of the other life that previously inhabited the upper layer of the ocean causing – gasp – change.

I am not very interested in their worries about too much life or their dread of the possibility of change.  My interest is that these researchers claim to have “quantified” not only the number of microscopic cells living on all of the little bits of plastic floating in all of the world’s oceans, but to have “quantified”  the “the total amount of carbon biomass in these  plastic-associated cells”.

How did they do that? 

From their paper:

“In situ incubations consisted of placing postconsumer plastic from 1-gallon milk jugs (PE), disposable cold-drink cups (PP), disposable hot-drink cups (PS), and glass cubes off a dock in Woods Hole, Massachusetts, in Vineyard Sound (GPS coordinates: 41.525, –70.673). The items were cleaned and then sterilized using 70% ethanol prior to placing them in the seawater, ~1 m below the surface in July 2013 in 1-cm mesh nylon cages to prevent plastic samples from escaping. Subsamples (~5 × 5 mm) were taken at periodic time points (1, 2, 3, 8, 12 weeks of immersion).”

They what?  They put pieces of different plastic (and in one case, a glass cube) in little plastic mesh cages and hung them off a dock at Woods Hole, Massachusetts.    They left them there for 3 months, periodically taking little samples from each.   They used the fancy  confocal laser scanning microscopy   to count the cells and types of cells on each piece.  And then:

”Although several studies have surveyed microbial diversity and quantified specific members of these biofilm habitats, ours is the first to holistically quantify total cell inventories under in situ conditions.    . . . .    Based on the reported plastic counts and size classes floating in the world’s ocean and the general abundances of different plastic debris in ocean surface water, we estimate that PMD [Plastic Marine Debris] could provide a total surface area of  2.5 × 1010 m2 (Table S4).

Integrating over the calculated PMD distribution in the world’s ocean, we estimated the total number of cells on plastic debris to be 2.1 × 1021 to 3.4 × 1021.  

Multiplying plastic surface area by the area-specific carbon biomass at the early and late stages of biofilm on plastic substrates, the total amount of carbon biomass in these plastic-associated cells is predicted to be 1.5 × 103 to 1.1 ×  104 metric tons, which is roughly similar with the previous  estimate of living biomass (8.6 × 102 to 1.6 × 104 metric  tons) on PMD. Our higher bound carbon estimate (1.1 ×  104 metric tons) approaches the estimated cellular carbon  mass in the global rivers (2.4 × 104 metric tons), as well as  both polar regions (8 × 104 metric tons).”

That’s right, using their single-location, one-time samples,  they have calculated, quantified, the total living biomass to be found on all of the plastic bits in all of the world’s oceans

Marvelous, isn’t it?   Who would have thought it would be that easy to guess the total weight of all those little microscopic plants and animals on the trillions and trillions of (uncounted) little bits (of unknown sizes) of plastic swirling around in the oceans. 

I have no idea of the accuracy of this research group’s counts of microorganisms living on the bits of plastic they hung off the dock at Woods Hole.   

But as for the rest, the magical mystical calculations based on things uncounted and unsampled? 

I call that:

Computational Hubris:

“An inordinate and unjustified trust, or faith if you like, in the power of advanced computational machines and processes to produce highly accurate and extremely precise results from relatively inaccurate and imprecise, highly uncertain data using techniques and methods that have not been tested nor verified to be suited to, or sufficient for, the purpose.”

— Kip Hansen

They have not only manufactured the quantities but they have manufactured a threat from their manufactured quantities. 

And that’s no way to do science. 

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Author’s Comment:

All of you who have experience snorkeling in tropical areas, or using SCUBA*, even in colder waters, will know that to turn a “sand desert” into an underwater oasis only requires the placing of almost ANY solid object on the sea floor.  Even a single rock the size of an orange becomes a mini-sea-life oasis, with plants, animals and fishes.  Sink a WWII destroyer and you have a huge living reef in a few months. 

This story tells us that even bits of plastic floating around in the top couple of meters of the seas, almost all smaller than 8 mm (3/10th inch) and most smaller than 4 mm (just over 1/10th inch), become homes for sea critters of all kinds.   The story fails to tell us that many of those critters are actually using the plastic not only as a home, but as a food source.  And, of course, many critters are eating the other living things on the plastic bits or using their biological excreta as food.   

I trust that the purposes of Nature will be fulfilled. And providing novel homes for more life probably isn’t a bad thing.

As an aside, this research is done in the relatively cold waters of Woods Hole, Mass.  They get a little thin biofilm over 3 months.   The bottom of my boat, despite poisonous anti-fouling paint, would collect inches of living material every month in the Virgin Islands – all kinds of growths and sea creatures that lived on and in the growth.  While cleaning the bottom one time, a little crab crawled into my ear, scuttling sideways. 

Remember, just because Nature will clean up our messes, given enough time, we should keep all of our trash, including plastics, contained and disposed of properly.  None of it should end up in the sea. 

Address you comments to “Kip…” if speaking to me.  Thanks.

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* = Self Contained Underwater Breathing Apparatus

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October 25, 2020 at 08:53AM

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