One Key To Healthy Oceans? Sharks : Short Wave Shark scientist Melissa Christina Marquez explains just how important sharks are to keeping the oceans healthy, including their role in mitigating climate change. Plus, there may be some talk about shark poop.

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One Key To Healthy Oceans? Sharks

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One Key To Healthy Oceans? Sharks

One Key To Healthy Oceans? Sharks

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You're listening to SHORT WAVE from NPR.


SOFIA: Melissa Cristina Marquez has been obsessed with sharks since the very first time she saw one as a little kid on TV during - you guessed it.


UNIDENTIFIED VOICE ACTOR: Shark Week starts Sunday...

SOFIA: So she was watching a show called - and this is real - "Air Jaws."

MELISSA CRISTINA MARQUEZ: Which essentially is just showing the power of great white sharks breaching, or flinging themselves out of the water, up into the air to kind of catch their prey...


UNIDENTIFIED PERSON: They're twisting and turning as if it is trying to dismember its prey.

MARQUEZ: And, you know, I think for any person, but especially a child who's never seen a shark like that before, it's really awe-inspiring. You kind of just sit there with your jaw on the ground being like, wait. What?


UNIDENTIFIED PERSON: To see such a spectacular...

MARQUEZ: It kind of cemented for me, as a kid, being like, yeah, this is what I want to study. This is what I want to dedicate my life to.

SOFIA: And she does. Melissa's a shark scientist, a Ph.D. candidate living in Western Australia. And what Melissa wants us to know is that sharks are not only these fierce and amazing creatures, like how she first saw them on TV as a kid, they also play this incredibly important ecological role, too.

MARQUEZ: The saying is, a healthy ocean needs healthy sharks. And that is very, very true.


SOFIA: So today in the show, we dive into the importance of sharks with shark scientist Melissa Cristina Marquez, including their role in mitigating climate change. And you know, there may or may not also be some talk about shark poop. I'm Maddie Sofia, and you're listening to Shark Wave from NPR.


SOFIA: All right, Melissa, let's get into it. Let's talk about something people might not think about when they think of sharks, and that's the role that they play in the health of the oceans.

MARQUEZ: Yeah. So let's start with kind of a generalized shark. Many of them kind of start their life out in a nursery - so in a secluded kind of area such as, say, a mangrove. And so they use the protection of those roots to kind of learn how to become a shark, to be able to hunt while not being hunted by their own species sometimes. Once this animal kind of grows up, some of them do go to coral reefs, and coral reefs need sharks. Just a shark being there actually kind of changes the dynamics of that coral reef.

For example, in Fiji, there are some fish that are herbivorous that eat kind of like algae and seaweed that's in the coral reefs. They'll actually avoid areas that are patrolled by reef sharks. So that means that the seaweeds have a chance to have kind of like a refuge in that area because they're not being eaten by any fish there. So it allows for that dynamic to exist.

SOFIA: Oh. I didn't - so they're actually - I'm not thinking of them, like, protecting, like, plant species, but just them being there is doing that.

MARQUEZ: Definitely - it is. It's one of the things of just a shark being there changes what a habitat looks like because it influences the behavior of the fish that they eat.

SOFIA: Right, right. And I know that they also kind of feed on the dominant prey in that area and that that can cause changes in those species. Tell me a little bit about that.

MARQUEZ: Quite a lot of people, when they think about - why do we need sharks? - they think of them keeping the ocean system balanced. And they do keep prey numbers balance. So for example, say you have a big predatory fish, and you have multiple of them 'cause you've taken out the sharks that prey on them. That means that that vegetation or any of those herbivorous fish that have kind of been protected or kept in check, suddenly, that whole entire system goes out of whack because you've got nothing keeping those other predatory fish in line. So they're kind of like, right, it's a smorgasbord. I can eat whatever I want. And really, it just leads to a ruined ecosystem.

SOFIA: So sharks play this role at coral reefs. And then they kind of, you know, start to migrate, start to move. What role do they play while they're actually migrating?

MARQUEZ: So the really cool thing about sharks is quite a lot of them are migratory. So they're not always in one location for their entire lives. Many of them, such as whale sharks, take really long migrations, so they pop up in various parts around the world. And so it helps kind of transfer nutrients from different parts of the ocean via, well, poop.

SOFIA: (Laughter).

MARQUEZ: If you think about it, it kind of makes sense 'cause their poop sort of acts like a fertilizer of sorts for any respective habitat. And a good example of this, there's actually gray reef sharks that are in the Central Pacific. And they forage offshore of their habitat at night, and then they return to kind of rest in this atoll during the day. And so they're constantly kind of shuffling nutrients from that outer open ocean area into a more densely populated coral reef area.

So researchers actually estimate this day-to-day offshore water-inshore water migration actually brings in about 95 kilograms of nitrogen daily onto a coral reef, which is usually nutrient limited, which means that it keeps this ecosystem pretty healthy. So yeah, I don't think we're going to be seeing, like, shark poop fertilizer any time soon in our stores. But...


MARQUEZ: ...It's good fertilizer.

SOFIA: I mean, it's wild that - like, how much nutrients that is actually introducing from its original location to the new location that might not have that. I mean, that's huge. I had no idea. I mean, poop's important always. But...

MARQUEZ: Yeah, 95 kilograms of nitrogen. That's - it's bananas.

SOFIA: (Laughter).

OK. So do sharks have any role in mitigating climate change? 'Cause I'm thinking - you know, I'm thinking about coral reefs. I'm thinking about the changing oceans right now. Are sharks going to help us out with that?

MARQUEZ: Yeah, definitely. There's actually a really great example of it here in Western Australia. So we've got a few tiger shark species, which is my favorite species of shark, and they patrol the seagrass beds here in Western Australia. And it seems to cause two specific animals to limit how much seagrass they eat. So sea turtles, which many people know, but dugongs, which are kind of like a relative of the manatee. So you're probably wondering why the diet of these two animals has anything to do with climate change. But essentially, them not being able to eat seagrass increases primary production, which is CO2 uptake, which maintains carbon sediment stocks. And marine sediments are one of the most expansive and critical carbon reservoirs on the planet, so they're key for regulating climate change.

SOFIA: Wow. So it's really, again, them just playing that role of creating a balance, right? That's - it's - when you think of sharks, you don't - the first thing you think in your mind isn't really, like, they help balance this ecosystem.

MARQUEZ: Yeah. You know, it's one of those things - when a lot of people think of sharks, they think of, oh, they just eat fish, and they keep that food web balance. And it's true. They do do that, but they do so much more that a lot of people don't realize. It's not until you kind of lay everything out on the table that they're like, holy crap, these animals do a lot. Yeah, we need to protect them.

SOFIA: Yeah. I mean, yeah, that's my - kind of leads me to my next question, Melissa, which is, you know, with all of this in mind, what is the - you know, the general state of sharks? You have convinced me they're super important for all different types of reasons. You know, are they OK? - I guess is what I'm asking.

MARQUEZ: I mean, it really depends the specific shark you are talking about because there are over 500 different species of sharks out there, which is really cool. And you know, they've been around for over 400 million years. They've survived multiple mass extinctions. But it seems that they're not really surviving the most formidable opponent, which is us.

A recent study that just came out is probably one of the most - largest collaborative projects that I've seen yet, was looking at the impact that threats such as overfishing and bycatch, habitat destruction and degradation, climate change, plastic pollution and, of course, illegal shark finning - what those kind of threats have on our global shark populations.

So it's bad. It was a bit sobering. And I did have a little bit of a cry 'cause, you know, as a shark scientist, I love these animals. I love learning about them. I love protecting them. But it does kind of get you a reality check of, I'm not going to be able to save them all. We're not going to be able to save them all if this continues. So that's why I'm a really big advocate of get rid of the jargon of, they're man-eaters, that they're monsters, that they're mindless killers because, if anything, if we're looking at the numbers, on average, they fatally bite six people per year, and we're killing millions of them a year. So really, if we want to label someone a monster, I think we're labeling the wrong animal. So they definitely need a PR manager.


MARQUEZ: Add that to my business card.

SOFIA: OK, Melissa, I want to end on a note of straight-up shark appreciation. So don't think too hard about this - really quick, give me your top three sharks. Go.

MARQUEZ: Oh, OK. Tiger shark - hands-down favorite, blacktip reef sharks and Caribbean roughshark - so if people Google that, it is a weird-looking animal.

SOFIA: OK, Melissa. This was super fun. I learned a lot. I appreciate you, and I appreciate sharks.

MARQUEZ: Thank you so much. Thanks for having me.


SOFIA: This episode was produced by Brit Hanson, fact-checked by Ariela Zebede and edited by Viet Le.

I'm Maddie Sofia. Thanks for listening to SHORT WAVE from NPR.


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