Parrotfish poop beaches and an altitude adaptation: Tiny Show and Tell Us #1

Tiny Matters

In this episode of Tiny Show and Tell Us, Sam and Deboki cover the role parrotfish poop may play in your next beach vacation and how the molecule 2,3-BPG helps people adapt to high altitudes and more.

Want your Tiny Show and Tell featured? Email with some science news you’re itching to share, a cool science factoid you love telling friends about, or maybe even a personal science story. In every 'Tiny Show and Tell Us' episode, Deboki and Sam will read your emails out loud and then go a bit deeper into the tiny science of it all. 

Transcript of this Episode

Sam Jones: Welcome to the first episode of Tiny Show and Tell Us. I'm Sam Jones, I'm the exec producer of Tiny Matters, and I'm here with my wonderful co-host, Deboki Chakravarti. Deboki, how's it going?

Deboki Chakravarti: Good. I'm excited to do this. We've been talking about this for a while, and so I'm so excited to actually be sitting down and going through things that people sent us.

Sam Jones: Me too. Finally making it happen. For those of you listening who are not regular Tiny Matters listeners, first off, we're glad you're here. Second, there's this thing that we do at the end of every regular Tiny Matters episode called the ‘Tiny Show and Tell.’ And so in that, Deboki and I each bring a piece of science news or a story that we recently read and we share it with each other, and now we want you to share with us, hence the name Tiny Show and Tell Us.

Deboki Chakravarti: So for these bonus episodes, send an email to with a science story, some science news you can't stop thinking about, maybe a science factoid and we'll read it aloud and then we're going to dive a bit deeper into it. So that's We'll put that in the episode description as well.

Sam Jones: And before we get into things, a huge thank you to Anne Hylden for doing research for this episode. Anne is a science writer and chemist who's working with Tiny Matters for the next few months. Okay. Deboki, should we do this?

Deboki Chakravarti: Yeah, let's do it.

Sam Jones: Okay. So I'm going to go first because I want to start things off on a pretty light, silly note.

Deboki Chakravarti: Cool.

Sam Jones: Our first Tiny Show and Tell Us is from listener Dakota who wrote in saying, "My fave science fact is that parrotfish eat coral and poop out calcium carbonate, which is what white sand beaches are made of. Your favorite beaches are poop." Thank you, Dakota.

Deboki Chakravarti: I mean, but isn't everything poop?

Sam Jones: Yeah. Yeah. It all comes back to poop, really. So first I want to say I had no idea that sand was really about size more than anything. So if more than 50% of the material is larger in diameter than 75 microns, which is about 0.03 inches, but smaller than 0.18 inches, it's sand. It's that simple. I don't know-

Deboki Chakravarti: Where do they get the size? Where were they like, "This is the cutoff that makes sense."

Sam Jones: They just said, "We're going with it." So I guess if the average particle size is smaller, it's considered silt or clay, and then if it's bigger, it's gravel. So not directly related to this, but I just thought that was really a weird and kind of fun thing. So what sand is actually made of really depends on where you are and what minerals are around. A lot of beaches are a tan color. I think growing up in the New England area, we don't have white sand beaches, at least to my knowledge.

Deboki Chakravarti: No parrotfish poop in our beaches.

Sam Jones: No, they're mostly like a tan-ish color, and that comes from a combo of iron oxide and a group of minerals called feldspar, which is cool. And then black beaches are black from obsidian, which is a volcanic glass that forms when lava comes out of a volcano, cools really rapidly. Just a little more on sand and beaches.

But today we're obviously focused on white sand beaches and parrotfish. So parrotfish are a group of fish species. They're not, I always think like, oh, it's a type of fish, but it's actually a bunch of different species and they're pretty decently sized. They're generally around 12 to 20 inches long. That's not a small fish, but some can grow to over a meter long, which is pretty impressive.

And so what they do is they eat algae off of dead coral or rocks, but their beak-like mouths end up taking bites of the coral as well. And I guess Anne found that the green humphead parrotfish, one of the largest species, eats live coral polyps too. So as they digest this nutritious stuff, this algae that they're getting off the dead coral, they're also grinding up the inedible calcium carbonate coral skeletons in their guts, and then they're excreting it as sand. So that's how that works. And apparently that humphead parrotfish can produce 90 kilograms, which is around 200 pounds of sand each year.

Deboki Chakravarti: 200, sorry, you said from one fish?

Sam Jones: Yes.

Deboki Chakravarti: It sounds like a lot when it's sand, but it's like even more when you realize it's poop.

Sam Jones: Oh yeah.

Deboki Chakravarti: Of course inevitably leads to the question of how much does the average human poop in a year?

Sam Jones: Oh it's so much.

Deboki Chakravarti: Yeah. I'm sitting here judging the parrotfish, but I don't know, maybe we must be pooping that much.

Sam Jones: Humans are producing way more than 200 pounds of poop a year.

Deboki Chakravarti: And we don't even get a beach out of it.

Sam Jones: No, I know. It's like what if we just pooped stuff to create beautiful beaches? Everything would be a beach though, really.

Deboki Chakravarti: I guess the argument is technically human waste can help fuel nutrients.

Sam Jones: That's true.

Deboki Chakravarti: And all of that. But I don't know.

Sam Jones: It's less aesthetically pleasing for sure.

Deboki Chakravarti: Yeah.

Sam Jones: So parrotfish are also not the only animals that poop calcium carbonate. I came across a study when I was just diving into it a little bit more from over a decade ago that found fecal samples from 11 common tropical fish, including barracudas, had a lot of calcium carbonate in their poop. And it appears some worm and oyster species also produce this calcium carbonate poop. That being said, parrotfish seem to produce a lot of it. And it's been estimated that up to 70% of the sand on white sandy beaches in the Caribbean and Hawaii has come from parrotfish poo.

So the Caribbean and Hawaii is really where you're finding this. I couldn't tell if it was exclusively or just the most, I think just depending on where parrotfish are, like where their actual habitat is, but in northwest Florida there are also white sand beaches and they do not come from parrotfish poop. They're actually nearly pure quartz.

Deboki Chakravarti: Whoa.

Sam Jones: Which eroded from the Appalachian mountains. So pretty cool stuff. So yeah, that's my dive into parrotfish poop. Thank you, Dakota.

Deboki Chakravarti: Wow.

Sam Jones: Yeah.

Deboki Chakravarti: I was not expecting the quartz.

Sam Jones: I know.

Deboki Chakravarti: That's really cool.

Sam Jones: That feels very fancy.

Deboki Chakravarti: Yeah, those are fancy beaches.

Sam Jones: Like northwest Florida, what?

Deboki Chakravarti: Yeah.

Sam Jones: I'd heard something about this at some point. It's one of those really fun little factoids that I think gets thrown out a bit, but I didn't realize 70% of the sand on white sandy beaches in the Caribbean in Hawaii come from parrotfish poo.

Deboki Chakravarti: Yeah. How did they estimate that? Do we know? I mean, someone must know how they came up with that number.

Sam Jones: I think that stat came from some survey that I found within the Department of Marine Biology, I think at the University of Hawaii where they're trying to quantify these things. But yeah, I would assume that if you have a sense of what is the population density of parrotfish in an area? How big are they? How much can we say they're producing? Because we know how much one fish can produce generally, can we then make an estimation for how much of that calcium carbonate is showing up on our beaches?

Deboki Chakravarti: Yeah.

Sam Jones: Yeah. It's cool. And it's not a deterrent at all. I think it's really cool. But now I want to go to the northwest Florida beaches that are made of quartz.

Deboki Chakravarti: Yeah. I feel like the thing that's weird about it to me, this is a brain thing, is I'm like the poop sand beaches probably don't hurt your feet and the quartz sand beaches hurt your feet.

Sam Jones: That's true.

Deboki Chakravarti: I don't know if that's true, but that's how my brain reads the situation.

Sam Jones: Yeah, because when you're like shredded quartz? But I guess if it's rolled around in the ocean for long enough like sea glass, I'm sure it's fine. But if anyone wants to write in about that, we will read it. So please do.

Deboki Chakravarti: Tell us about the quartz beaches.

Sam Jones: Yeah. Do you live in northwest Florida and how are those beaches?

Deboki Chakravarti: Yeah. Okay. So our next Tiny Show and Tell Us is from our listener Mike. I'm just going to read what he wrote, but when I say I, it's Mike. I used to live in DC but moved to Colorado a few years ago. When living in DC I would bike and run with a friend who was always quite a bit faster, but gracious enough to keep my pace. That's a good friend.

Sam Jones: Yeah.

Deboki Chakravarti: After a few years of living in Colorado, he was coming out for a visit. Given that I had ample time to adapt to my mile-high environment, I thought maybe it was time to be the quicker one, or at least keep up. This did not happen. I was still on the struggle bus.

Sometime later, my father-in-law was talking about how quickly the body can adapt to changes in altitude, and specifically mentioned how the body produces a molecule called two three BPG to quickly increase the amount of oxygen that red blood cells can deliver to our tissue when going to a higher altitude. I'm pretty sure I would've been outpaced even if my friend didn't have this little molecular helper. But it is fascinating to learn about all the amazing things that are happening in our body and how much scientists have been able to discover.

Sam Jones: That's cool.

Deboki Chakravarti: I mean, totally. I feel like all of these things are like, they're so invisible, and then you're just realizing, "Oh yeah, this kind of makes a big difference." And that's something that was really interesting kind of diving into this.

So2,3-BPG is short for 2,3-Bisphosphoglyceric acid and I hosted Crash Course Organic Chemistry and so all of these molecules, I remember just sitting there for 10 minutes just being like, "I got to say this again and again and again and again and again to try to get the pronunciation right." And then inevitably it would come up on the teleprompter and I would be like, "Mind blank. Don't know how to say this word. Vowels don't mean anything to me anymore." So anyways, this is fond memories.

OK, so one of the things that two three BPG, which is what I'm going to just call it, can do is regulate the activity of an enzyme by binding to it. And specifically in this case, what it's doing is regulating the activity of hemoglobin, which is a protein in our red blood cells. It's made up of four subunits that bind to oxygen, and there are two alpha subunits and there are two beta subunits. And one of the things that apparently can happen is that when beta subunits aren't bound to oxygen, they make this nice little pocket for 2,3-BPG to bind to, and that kind of changes the affinity of hemoglobin for oxygen overall.

So what happens is if you're in a low oxygen environment, 2,3-BPG will bind to those deoxygenated subunits and actually lower its affinity for oxygen. So what that means is that will cause the other subunits to release oxygen. So by lowering the affinity overall, it's like you're releasing oxygen out. So again, because you're in that deoxygenated environment, you are making it so that your hemoglobin will be more likely to release oxygen to the tissues that need it.

Sam Jones: Oh, that's fascinating.

Deboki Chakravarti: It's really cool. It's like Mike said, it's wild like that there are these little molecular mechanisms that just work. And so one of the places that this comes up in is at high altitudes. It also goes up with exercise also. It goes, 2,3-BPG concentrations, go up during pregnancy because it's a way to get more oxygen to the fetus.

Sam Jones: Yeah, that makes so much sense. It's so smart. It's such a smart adaptation.

Deboki Chakravarti: Yeah. I feel like a lot of these things, you're like, "Well, all I need is the hemoglobin. I just needed to carry oxygen." And then you realize, "No, this stuff is specially adapted to make it possible to do a bunch of different things."

Sam Jones: Yeah. Huh. With all of these kinds of really cool adaptations, it makes me think a lot about, “how did this come to be?” What were...I think altitude is an obvious one. I mean, I guess all of these things, right? It's like altitude, pregnancy. For us, we're like, "Exercise", but our ancestors were like, "Exertion because we have to run for things. We're not going to Orangetheory, guys. We're hunting for food."

Deboki Chakravarti: Yeah, for sure. I was also really curious, I don't know if our listeners know this, because I probably haven't mentioned it, but I am pregnant, due in a month from when we're recording this, so the oxygen thing I appreciate because it's hard to breathe. People really undersold to me how weird breathing becomes very quickly, because so much of your oxygen is going to this tiny growing thing.

So I do appreciate what little effect, I assume there's a big effect because I assume breathing would've sucked a lot more without the 2,3-BPG. Pregnancy obviously you just learn that there's a like bajillion molecules that suddenly become active that they weren't doing before.

Sam Jones: Yeah. Hormones are wild and yeah, certain bodily shifts for sure.

Deboki Chakravarti: Right.

Sam Jones: Yeah, I think this is really fascinating. I think another thing was, it seems to be unclear how long this effect lasts. Of course, if you're pregnant, the fetus is there, right? But with altitude, it's like you have other adaptations, and maybe actually when you're pregnant, there are other ones as well.

So I wonder how quickly, depending on the circumstance, depending on the environment, how quickly does this all of a sudden start to kick in, right? If I'm going to go on a run this afternoon, I assume this is going to start kicking in pretty quick, but as soon as I stop, I assume then my body, maybe it's once I get back to a certain, I don't know, heart rate or how much I'm sucking in oxygen, I want to know what are the little alarm bells that go off to your body where it's like, "All right, let's start doing this thing."

Deboki Chakravarti: Yep. What is the regulator of the 2,3-BPG concentration in general? What does that feedback mechanism look like? Does it get trained? Obviously, people adapt to different environments.

Sam Jones: It also makes me, this is like a darker path to go down, but it also makes me wonder about certain drug use among, you know the Olympics is coming up, it makes me wonder how some of those drugs that you hear about that do have to somehow deal with oxygen availability, storage. How does that then impact 2,3-BPG?

Deboki Chakravarti: Good question.

Sam Jones: Right? What is the interplay there? Do some actually increase that? Or is it something completely different and then all of a sudden your body is maybe not going to do this thing with two three BPG? I'm going down a more pessimistic route of human manipulation.

Deboki Chakravarti: Okay. So I did a very quick Google, and there are papers from the seventies about manipulating, oh no, this is DPG. I don't know what DPG is. Diphosphoglycerate.

Sam Jones: Oh, no. So it looks like two three BPG is also known as two three DPG.

Deboki Chakravarti: Okay. So interesting.

Sam Jones: Because bi- and di-phospho is really the same thing, right?

Deboki Chakravarti: Sorry, I should have put that together.

Sam Jones: No, I just seeing it written out, I'm like, "Oh, yeah, okay. Two."

Deboki Chakravarti: So yeah, there are papers about this. Let's see. So it seems like scientists have looked at manipulating the concentration, so apparently you can manipulate the concentration of 2,3-BPG with a steroid.

Sam Jones: Huh.

Deboki Chakravarti: Interesting.

Sam Jones: Wow. I'm really onto something. 50 years later.

Deboki Chakravarti: You were about to peace out from Tiny Matters — “You guys, I've got a great idea for athletic performance enhancement."

Sam Jones: Oh my … just lose all credibility in three seconds.

Deboki Chakravarti: Well, I'm glad that you had that darker thought because that was interesting to see. It's interesting also to me that all these papers that are coming up on Google are from the seventies. Obviously, who knows if that means anything. Google Search results mean so little now.

Sam Jones: Yeah, that's true. Again, if someone knows more about this-

Deboki Chakravarti: If you've taken steroids.

Sam Jones: No, we don't want to be implicated. Please don't send us anything incriminating. But beyond that, if you know things about this, write in. We want to hear more.

Deboki Chakravarti: Yeah, totally.

Sam Jones: Okay. Let's wrap up the end of the first one.

Deboki Chakravarti: Yeah. Oh, that was fun. 

Sam Jones: Thanks for tuning in to the first Tiny Show and Tell Us, a bonus episode from Tiny Matters, a production of the American Chemical Society. And thank you again to Anne Hylden for her work on this episode.

Deboki Chakravarti: Send us an email to be featured in a future Tiny Show and Tell Us episode, You can find Sam on social @samjscience, and you can find me @okidokiboki. See you next time.

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