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In the 1990s, researchers were puzzled by struggling trout populations in the Great. Lakes.

Even though pollution levels were low, the fish were acting really weird. They were having a hard time swimming upright, and showing signs of overexcitability all very strange behaviors for these fish. And they weren’t just acting weird.

A not-small number of them were actually dying before they could reach adulthood — and no one could really figure out what was going on. That is, until a team of researchers suggested that these fish might be missing something important: vitamin B1, often referred to as thiamine. And it turns out that hunch was right!

When they supplemented their diet, the fish recovered. Only... it turned out it wasn’t just these fish. Since this initial discovery, scientists have found dozens of other creatures living in the Northern Hemisphere which were similarly lacking thiamine including fish, birds, reptiles, and maybe even mammals.

Some experts think that’s evidence that something much bigger is going on: that nature has a vitamin deficiency! And that’s led to a flurry of research into what could possibly be causing this impending ecological crisis. And… well, spoiler alert, the studies basically all point a finger at humans being the problem… though, in different ways.

And ultimately, while these deficiencies themselves are a big problem, they’re also an indicator of an even bigger one: a planet under stress. Thankfully, now that scientists are aware of the potential crisis and have some solid ideas for what could be causing it, they can move forward with trying to alleviate it — before it's too late. Now. if you’ve heard of thiamine before , it was probably because of a multivitamin or health supplement.

That’s because thiamine is an essential nutrient for all organisms. But we animals can’t make it. Only plants and some fungi and microorganisms can.

The rest of us have to get thiamine by eating those thiamine makers, or by eating something else that has. Basically, the vitamin slowly spreads up the food chain. Physiologically, thiamine is important because it helps your cells turn the food you eat into fuel that your body can use.

It’s involved in the chemical reactions that mitochondria use to generate energy for the cell. So, without thiamine, an organism’s cells are simply unable to turn food into cellular fuel. And a severe thiamine deficiency will eventually lead to illness and death, because cells basically stop functioning.

But what’s especially awful about thiamine deficiencies is that even mild ones can have nasty effects. Like, strange behavioral issues, as scientists observed in the Great Lakes trout. That’s because brain cells need a lot of cellular fuel, so they’re extra sensitive to low thiamine levels.

And these quote “sublethal” effects can vary widely, so it can be super hard to diagnose what’s really happening — which makes it harder for people to act quickly, before the problem becomes much harder to solve. Now, scientists have known for a really long time that a thiamine deficiency is a huge problem for people. For example, the disease beriberi, which is caused by a lack of thiamine, was first described by Western physicians in the mid-1600s.

But in part because it’s so tricky to spot, it wasn’t until the 1990s that thiamine deficiency was discovered to be a big problem for wildlife, as well. Those struggling Great Lakes trout populations got a lot of people thinking about thiamine in wild animals. And once they were aware of the potential issue, researchers found deficiencies in all sorts of other creatures.

This included other underwater inhabitants, like alligators and mussels, as well as land animals, including dozens of kinds of birds! Of course, when people lack thiamine, the usual fix is to change their diet or give them a supplement. Unfortunately, those don’t really work for ecosystems.

Even if we could figure out how to dole out a supplement, it’d be like slapping a tiny bandaid on a gaping wound. So, in order to devise a solid, long-term solution, researchers need to get at the root cause for the deficiencies. And, well, it’s kind of taking awhile to figure that out because there are likely multiple things going on.

For starters, in some areas, there seem to be shifts happening in those tiny critters that can make their own thiamine. For example: a study in 2012 of the southern California-Baja coast found that there was a lot more variability in B vitamins than other commonly found nutrients. The researchers think that’s because climate change is messing with ocean circulation patterns, which in turn is altering the abundance of certain microbes.

You see, researchers think that, in the ocean, the microbes that make thiamine are often found in deeper waters, since that’s where they get the parts they need to make it — like, dead plankton. So, the thiamine they make wouldn’t get into shallow water unless they’re dragged up from the depths — like, in places where ocean currents move deeper waters to the surface. And that’s where the system is starting to break down.

As the Earth’s atmosphere gets warmer — you know, thanks to us and all those greenhouse gases we keep producing — the ocean gets warmer as well. But this warmth isn’t evenly distributed — the top layer of the ocean is absorbing a lot more heat than the depths. And these much warmer waters not only float on top of the colder waters, they don’t mix well with the lower layers, leading to a phenomenon called stratification.

And this stratification seems to be limiting the upward movement of the thiamine-producers! ~. So, they’re not ending up where the creatures who need to eat them can easily get to them. Changing water conditions may also be creating an environment that selects for organisms that can’t make thiamine, or are inedible.

You see, a study published in 2020 looked at thiamine deficiencies in Baltic salmon and found that changes to water conditions, especially things like nutrient input, had led to a shift in the food web. Suddenly, certain kinds of cyanobacteria largely replaced the organisms that had served as the bottom of the food chain. And while these cyanobacteria are rich in thiamine, they’re also not really edible.

So none of that thiamine was available to the animals in the food web. This kind of fundamental shift of aquatic microbes may also help explain why some birds are suffering from thiamine deficiencies. Though, not because they eat plankton — but because their prey do!

Take eiders — a seabird fond of mussels. Researchers discovered that these birds and their favorite food were both lacking in thiamine in the mid 2010s. And mussels are filter-feeders that vacuum plankton out of the water — so it tracks that a change in microorganisms could underscore their thiamine deficiency.

But microbes may not be the problem everywhere these deficiencies are cropping up — or, at least not the only one. In 2019, researchers demonstrated how overfishing could cause thiamine deficiencies using a computer model. See, fisheries often target small plankton-eating fish — like juvenile cod, for example.

In fact, cod are one of the most popular fish in the United States, and Atlantic populations have declined in recent years due to overfishing. Well, this model showed that when young cod and other plankton-eating fish disappear from the food web, their prey populations increase. And these prey munch on the “animal plankton” or zooplankton that would otherwise be hanging around in the water.

So more of them means less zooplankton.~ And those zooplankton typically eat the tiny organisms that produce thiamine. So they’re the easy way for thiamine to get from the bottom of the food web to everyone else! But that means, if zooplankton populations drop, there’s basically no one to transfer this essential vitamin to all the other, larger creatures.

And, like with microbial shifts, this kind of deficiency could be impacting animals that live on land but depend on water-dwellers as a primary food source. Plus, it’s not the only way non-microscopic critters may be involved in deficiencies. Because some species make an enzyme called thiaminase.

Thiaminase breaks down thiamine, so it lets those species process thiamine that’s been damaged or degraded. Basically, it lets them get a little extra from the thiamine in their diet. But this enzyme can destroy perfectly good thiamine.

And if an animal eats food containing a lot of thiaminase, the enzyme goes to work destroying all the thiamine in its gut, keeping it from actually getting any from its meals! ~. Scientists suspect that this is what underlies recent increases in mortality of mammals that don’t love seafood — like pronghorns and... camels. This could make sense if their diet has shifted to one that’s heavy in grains — which promote the growth of thiaminase-rich bacteria in their stomachs — or if they’re munching on a lot of thiaminase-containing plants, like bracken ferns and horsetails.

Researchers know that can happen with livestock and captive animals like deer. And, thanks to our farms, there are plenty of grains around. Plus, those particular thiaminase-rich plants do pretty well in a warming climate, and may even outcompete other forage plants that are more sensitive to changing temperatures.

So, basically, our love of fossil fuels may be encouraging thiaminase-rich plants to grow, resulting in a dietary shift that could harm wildlife! And something very similar is already happening underwater. For example, a 2016 paper revealed that Chinook salmon in Western Alaska had lower thiamine levels when they ate thiaminase-containing fish like capelin.

And central California salmon are also lacking in thiamine, which was tied to a recent shift towards an anchovy heavy diet — another fish rich in thiaminase. And, in a paper published in 2005, researchers found that several salmon species in the Great Lakes were thiamine-deficient because they were eating too many thiaminase-rich alewife and rainbow smelt. And this is where it becomes really clear that, no matter what case you’re looking at, this is all ultimately our fault.

You see, both alewife and rainbow smelt don’t belong in the Great Lakes. They were introduced by humans! And even where people aren’t directly responsible for the presence of thiaminase-rich creatures, we’re probably to blame for their sudden abundance.

Like, we know the type of food available to Chinook salmon depends on the climate and how it affects the way water moves into the Bering Sea. So, all that CO2 we’re spewing and its effect on global climate are directly impacting what these salmon can eat. And the same goes for the California salmon.

Those anchovy populations exploded thanks to warmer water temperatures — which, again, is thanks to climate change. But the upside here is that we have the opportunity to fix what we’ve broken! The solution is probably not going to be a one size fits all type of thing — and yeah, curbing climate change is probably a big part of it.

But there are other things we can do, especially at the local level. For example, in Lake Huron and Lake Michigan, the fish issue was managed by adding thiamine to the water in hatcheries. You see, for a while now, both trout and salmon have been artificially bred and released into these lakes to boost their natural populations.

So researchers gave those baby fish a little extra thiamine. And not only did the fish not end up deficient as they grew up, they appear to have outcompeted the thiaminase-rich alewife, likely helping cause their numbers to decline! And researchers are working on finding solutions like that for everything we’ve talked about today.

Like, if a deficiency is exacerbated by overfishing, then altering what and how much we remove from an ecosystem could help shift it back in the right direction — or at the very least, ensure wild animals have enough of their natural foods to eat. And even in places where problems go all the way to the microbial level, we might have some options. Like, if cyanobacteria are taking over, then regulating the amount of agricultural pollution might help, as they flourish in runoff.

Or there may be some other way of cleaning up the water to get conditions back to promoting thiamine-makers instead. Getting rid of nature’s vitamin deficiency isn’t going to be easy. But all of this knowledge gained over the past three decades is helping governments and organizations move towards taking more sustainable approaches in managing ecosystems.

And researchers are continuing to investigate this widespread problem so they can come up with effective, attainable solutions. Thanks for watching this episode of SciShow! And thank you to everyone who supports this channel, whether it’s as a channel member here on YouTube, or as a Patreon patron.

We wouldn’t be able to dive deep into complex topics like this without your support! So thank you. And if you’d like to learn more about how you can help us make free educational science videos, you can find our patron community at Patreon.com/SciShow, or you can click the Join button below the video to get all the info about becoming a channel member here on YouTube. [ outro ].