How Do Mussels Get Their Shells?
24:18 Share

It's fall and many kids are headed back to school and they're on the hunt for the perfect book to read. Don't forget to check out our But Why book series. We have two books perfect for young readers about age 8 to 10. Look for Our Llamas Ticklish and Do Fish Breathe Underwater wherever you buy your books. And if you prefer to listen to books, check out the audiobook versions as well. You can find out more at butwhykids.org books.

But why is supported by Progressive, where drivers who save by switching save nearly $750 on average? Quote now at Progressive.com. Progressive Casualty Insurance Company and affiliates national average 12-month savings of $744 by new customers surveyed who saved with Progressive between June 2022 and May 2023. Potential savings may vary.

Some fish are really neat. My favorite fish of them all are called alewives. We call them anadromous. There's your vocabulary word for the day, anadromous. This is But Why, a podcast for curious kids from Vermont Public Radio. You ask the questions and we help find the answers.

I'm Jane Lindholm, and in this episode, we're taking the podcast to sea. We're heading to the coast of Maine to learn a little bit about why the sea is salty, how mussels get their shells, and why a lobster with no claws, no antenna, and no eyes will probably still come out okay.

and we'll find out what the heck anadromous actually means. My name is Zach Whitener, and I'm a research associate at the Gulf of Maine Research Institute in Portland, Maine. Today we're down at Kettle Cove in Cape Elizabeth with lots of pretty lobster boats in the distance and a wonderful place by the ocean. Cape Elizabeth is near Portland, Maine, and Kettle Cove is a sheltered little area with tide pools and a rocky beach in Cape Elizabeth.

Zach and I met there on a bright September morning not long after low tide. We originally made and aired this episode in 2016, but as we head towards summer and the end of the school year here in the Northern Hemisphere, we thought you might like to hear it again.

At high tide, a lot of the rocks at Kettle Cove are covered with water. But in low tide, when the water recedes, it exposes those rocks and some of the creatures that live in the shallow water. I think one of the most exciting parts about coming down to the side of the ocean is it's not just about the water. It's about...

the birds, and the people that are here too. As you can see on the rocks here, we have a lot of what we call rockweed or bladderwrack. Every place you go, you'll hear a different name for it. Lots of little animals underneath it. You'll find lots of crabs, sometimes even baby lobsters. We've got periwinkles and many, many, many different types of snails. We've got sea stars, sometimes sea anemones you can find in the tide pools, sometimes little fish. There's a lot of neat things you can find here.

If you've ever been to the ocean, you've probably discovered that the water in the sea is different from the water that comes out of your sink or even the water in lakes and streams. If you taste it, it's salty. But why? Hi, I'm Chase. I'm nine years old. I'm from Enfield, New Hampshire. I want to know why the sea is salty. Hi, Chase. I think that's a great question to ask.

What it really comes down to is that the ocean is the bottom of the, for lack of a better word, bottom of the food chain. Every stream in Brooknecks, your house in Enfield, New Hampshire, eventually it gets to the ocean. So not only do things like salt and mud, but also your pollution goes all the way downstream. I have to put in my plug for pollution. But the most important thing is that rainwater...

is actually slightly acidic, which surprises a lot of people, but it's because of a reaction between carbon dioxide and water creates carbonic acid. And so when it rains, the rain weathers rocks and pulls some of the ions or elements out of it, different minerals. And so it's not just salt, but lots of different things, but salt's the most common one. So the salt actually comes from the rocks, and it washes into the streams, and then washes into the rivers, and then down eventually into the ocean.

So since the ocean is the bottom of the line, excuse the pun, there's nowhere else for the salt to go. And so it builds up in concentration. Interestingly, it's not just the ocean that's salty. The Great Salt Lake, which is a famous lake in Utah in the western United States, that's very salty because of the fact that there's no outlet. There's no river that goes from the Salt Lake to the ocean. So all the salts from the rains out west, they go into the Salt Lake.

So to get back to the ocean, the ocean is about 35 parts per thousand salt, which means about three and a half percent. You can actually evaporate seawater to get salt. So the sum of the salt that we eat actually comes from ocean. Yep, the exact same salt. Unfortunately, because of pollution, you have to be careful which seawater you use to make salt now.

And when you're in the ocean, if you swim in the ocean, you might realize that you can float easier in the ocean than you can in a lake. And that's also because of the salt?

That's right. Because of the salt in the water, the water is more dense. It doesn't feel like it. If you just touch it, when you get your body in it, you float much better in salt water than fresh water because the salt makes the water heavier, so you don't have to displace as much of the salt water to float, which is why in some places with greater salt concentrations, like the Great Salt Lake or the Dead Sea in Israel, you float like a cork because there's so much salt in it.

Animals that live in the ocean are specially suited to surviving in this salty environment. But not every animal can do that. So for example, if you took a freshwater fish and put it in the ocean, it's not going to live. Because what's going to happen is its body is more fresh than salty, for lack of a better explanation. And so its body is going to soak up a bunch of salt. So since they can't get rid of that salt, it actually poisons them and they die.

Whereas if you took a saltwater fish and put it in the lake, what would happen is the lake, being freshwater, fresher than the salty body of the fish, would suck all of the salt out of the fish, which would also cause it to die. And so fish have evolved for different areas to regulate salt. A great example of salt regulation is actually with seagulls, the herring gulls that we have on the coast of Maine.

They have salt ducks on the top of their beak, and so their bodies are constantly extruding salt. That way they can survive in the harsh, salty environment. That's pretty cool. Those seagulls have a special adaptation that allows them to spend so much time floating and fishing in the salty water. But seagulls aren't the only animals who have special adaptations that allow them to go between salty and not-so-salty environments.

Zach's special area of focus as a marine scientist is with fish that live in both salty and freshwater environments. Some fish are really neat. My favorite fish of them all are called alewives. We call them anadromous, which means that they live in the ocean but spawn in freshwater. Just like a famous example that I hate to use is salmon. I hope someday everybody knows about alewives that I can use alewives for the example.

But alewives live in the ocean until they're ready to breed. So they swim up rivers and they go back to the ponds where they themselves were hatched. They spawn in the ponds and the juvenile fish, after a few months, swim back down the rivers to live in the ocean for a few years. And then they complete the cycle. They go back up the rivers.

What's really interesting about going back and forth between saltwater and freshwater is, first of all, physiologically, it's really strenuous on the fish. It's impressive that their bodies have found a way to go back and forth between fresh and saltwater. If it's so hard on their bodies, why would fish evolve to do this, to live in saltwater but go lay eggs and be born in freshwater? The ocean is a big, scary place for a fish.

Many, many, many things can eat you. So the alewives and other fish like that have learned that freshwater is a safer place to have your babies. But the problem is eventually you have so many babies, there's not too much to eat in a little lake.

So the juvenile fish know that it's in their best interest to swim downstream, to go out to the ocean, the buffet of the world. By then they're big enough that it's not quite so big and scary and everything's trying to eat them. Everything is still trying to eat them, but they do a better job as they get bigger in the ocean. Before we move on, do you remember what Zach said fish like alewives that live in saltwater but spawn or lay their eggs in freshwater are called?

Anadromous. Anadromous is a Greek word meaning running upward, which makes sense. I mean, fish don't have feet, of course, so they can't exactly run upward. But fish like alewives and salmon swim upstream against the current to lay their eggs in fresh water. So it makes sense if anadromous means running upward and fish are swimming upstream. Music

Coming up, we'll turn over some rocks to see what we can find in the shallows. And have you ever wanted to make a ship in a bottle? Well, we'll learn how it's done coming right up. This is But Why, a podcast for curious kids. I'm Jane Lindholm. Today, we're learning about why the sea is salty with Gulf of Maine Research Institute scientist Zach Whitener. Let's go back to the beach.

Can we look in a couple of the little pools here and see what we can find? Can you show me a couple of things? Sure. So this is not really a tide pool, but kind of. It's almost a tide pool, right? Yeah, it's a little one, but we can see what we find here. We've got a few different...

periwinkles here. Periwinkles, an interesting fact, these are actually invasive here. These are tiny little snails for people who are not familiar with periwinkles. The little brown snails that everyone sees as ubiquitous, which means they're everywhere. On the coast here in New England,

These are actually a non-native species that came from Europe many, many, many years ago. But now we see them as commonly as all the seaweed, and we think nothing of it. They're supposed to be here. And something like a periwinkle, a little snail, when you say came over from Europe, that could have come on the ships, right? It sort of sucks to the side of a ship and comes over that way? Yeah, they were probably stuck to the sides of ships that came from Europe, and they got over here and they stayed.

There's something that I used to call a lady slipper as a kid. Yep. What is that?

Monoplacophore? I don't know how to describe them. I mean, it kind of looks like half a clamshell, but then it has a little shelf inside of it, so you could sort of scoot something underneath it. Yeah, they're closely related to clams and mussels. It's basically a snail with a cave for a shell instead of being able to go up inside. And so they stick themselves to rocks, and they're very, very difficult to pry off if you or a fish or anything else trying to eat them were coming along.

And then there's some other kinds of snails, and I'm guessing you don't have an answer for this because nobody seems to have an answer for this. But when I was a kid, we were always told if you hum at a snail, it will come out of its shell. And from my experience, it works, but nobody knows why. I think there was recently a scientific study working at this.

And the conclusion was basically, if you hold a snail in your hand and hum at it, eventually it'll come out of its shell...

Or if you just hold it in your hand long enough, it eventually will come out of its shell. But what's the fun in that? Of course you should hum at it. Can we do it? See if it works? Sure. I have... Is mine a periwinkle? Yep. A big, large periwinkle? And what are you holding? Yep, this is also a periwinkle. All right, so are you ready to hum? I'm ready. Okay. See who wins here. Yours is already coming out. Quick, hum. Mine is coming way out. I know. Hmm.

Mine's got a bigger shell to try to move. Mine's going back in. Uh-oh, I'm not singing well enough. I don't know, Zach. Is yours coming out? It was starting to, then I picked it up. All right, so here I see...

a little mussel shell. And people may be familiar with these, right? They're sort of the bluey-black ones. This one has a barnacle attached to it. It feels pretty light. I think this one does not have anybody inside of it. But we did get a question from Lauren. How do mussels get their shells? My name is Lauren, and I live in Washington, New Hampshire. Well, when mussel eggs first hatch...

The larval muscle drifts around in the ocean for four to six weeks until it finds a suitable habitat, which means basically it's looking for a place where it can stick itself to the bottom and hopefully not get eaten, at least not too soon. So as soon as they attach to the bottom, the muscles actually already have the very beginnings of their shells attached.

And just like how when we eat food, we can use the nutrients in our body to grow our fingernails and our toenails, they grow their shells by taking nutrients out of the water. Interestingly, where a mussel lives will have an effect on how thick its shell is. In a place like this, in the inner tidal, where we have lots of predators like crabs and sea stars, the shells will be very thick. The mussels will put a lot of energy and effort into making big, thick, hard shells to protect themselves.

However, people have found that with mussel farms offshore, or ones that are just up in the water columns, they're not on the bottom, well, we found that when the mussels aren't around predators, they put very little energy into producing shells. So although they still have shells, they're very, very brittle. What scientists believe is that the mussels...

can smell their predators. They're called pheromones. They're chemicals in the water. Just like how we smell by chemicals in the air, mussels smell by chemicals in the water. And if they can't smell any predators, they have no cue. They have no instruction to build big, thick, strong shells. Zach says the size of a shell depends on the type or species of mussels, but it also depends on the age of the mussel. As the animals get older, their shells get bigger.

Since we were looking around in the tide pools, Zach wanted to see if we could find a little lobster. Sometimes young lobsters hide under rocks in the tide pools. This could be a lobster. But you see how it's dug out right there? When lobsters get under rocks, they'll excavate it more to make a bigger home for themselves. So you can see where something's been digging under this rock. I don't know if I can move it, but... Good muscles of the human variety. Doesn't look like anybody home today.

Oh, there's one. Here's a baby lobster, a juvenile lobster. I'm not sure at this size, but he's probably a few years old at least. A lobster isn't legal size until it's about seven years old in this area. When he says legal size, Zach means legal to eat. Lobsters are big business on the coast of Maine. In 2015, more than 120 million pounds of lobster was caught.

When a lobster man or woman pulls a lobster out of a trap, he has to measure from the lobster's eye socket to the edge of its body. If it's not at least three and a quarter inches long, the lobster has to be thrown back into the ocean so it can keep growing. Lobsters that are too big have to be put back too, by the way. So any lobster you see on someone's plate or in a tank at the grocery store that comes from Maine is at least about seven years old.

The lobster we found could fit in the palm of Zach's hand, but as he said, it was already a couple of years old. When he looked a little closer, Zach noticed something really weird about this guy. This guy actually doesn't have any eyes. Somebody has been preying on him, you think? Yeah. He lost his eyes and his claws, but he can still eat and he's still alive. Quite alive. No antennae, so I bet another lobster...

Clamped right on the front of him. Poor guy. Actually, yep, this is a male. So will he survive? He could. Clearly, he's been living for a little while because these aren't recent injuries. You can tell just from the way that there's kind of scar tissue over the missing appendages, over the missing claws, and over the missing antennae. He's clearly still living. He's finding things to eat, hiding under this rock. I'll put him right back under it to keep him safe.

Lobsters can regrow their limbs, so eventually his claws will grow back and his antennae. I've got no idea about their eyes, though. It's really interesting. I wish him the best of luck. If the only lobster you've ever seen has been cooked, you might be surprised to find out that lobsters aren't red, at least not when they're alive. Their shells turn an orangey-red color when they're cooked. But lobsters are naturally a sort of dark, bluey-green color.

Before he became a scientist, Zach actually grew up in a family of lobstermen. That's what got him interested in the first place in becoming a marine researcher. I grew up lobstering in Long Island, Maine, which is in Casco Bay off of Portland. And so I started lobstering when I was 10 years old and...

I was just wondering, why are there more lobsters here in this channel or there behind that island? Beyond just the migrations that the lobstermen have pretty well figured out. In June they go here, in July they go there.

I was very interested in what attracts the lobsters to different places. I first got involved in research when I was, I believe, 16 years old. I got a temperature sensor from a scientist at the Woods Hole Oceanographic Institute, and it logs the temperature once an hour. And so I put it in one of my lobster traps for him and kept a record of what I caught. And so he did this with, I think, 10 lobsters from up and down the coast of Maine.

The study showed that the temperature of the water on the seafloor where lobsters crawl around changes a lot, even from hour to hour, and that can affect where lobsters go. Being part of scientific research as a teenager got Zach interested in becoming a scientist himself. So he went to school to become a researcher, and now he says he's doing what he loves.

All this talk of the sea has us feeling quite nautical. And as you listen to those waves roll in and out, maybe you are thinking of big sailing ships on the sea. Some people like to capture that feeling and put it in a bottle. Have you ever been to a museum or someone's house and seen a glass bottle lying on its side with the model of a ship inside of it?

Well, I'm not the only one who's wondered, how did that ship get through that bottle's tiny opening? My name is Nico from Nashville, Tennessee. I am seven years old, and I want to know how people put a ship in a glass bottle. My name is Daniel Siemens, and I'm a ship and bottle builder out here in Colorado.

I got into building ships and bottles because I watched Pirates of the Caribbean actually. In the fourth movie, Blackbeard has all those ships and bottles in a cabinet and stuff. And I thought at the time, I was like, how do they get ships and bottles? And so I went online and I started looking around and I figured it out. And after you do a couple, you just get hooked. It's just too much fun.

The first step is finding the bottle. The bottle is pretty important as far as building the ship goes because you build the ship to fit the bottle. What you're looking for is the clarity to make sure you're able to see the ship pretty well through the bottle. Some bottles are just not clear enough.

So then it's a matter of sizing out the plans. Some people will draw them out. Some people will – like I will find plans and print them off and I will set my printer up to print bigger pictures or smaller pictures and kind of size it out and I will put those pictures in the bottle and see does this fit and pull them back out and try different things.

So sizing the plans to the bottle is the next step. Then you start building the ship and the entire ship is built outside the bottle before it ever goes in. Everything, the mast, the rigging, all of it is all built outside the bottle. I use basswood for the wood. It's pretty easy to carve. And bamboo skewers work great for the mast because they're really strong and you can whittle them down really, really thin.

Fly tying thread for the thread for the rigging and the rope side of it. And paper, actually, for a lot of different things. I use paper for windows or different really fine details. A lot of ship and bottle builders actually will go out and find all sorts of crazy materials. Like I've used the black wire and a cell phone charger cable to do cannons because it's nice and round and it's already black so I don't have to paint it.

The model is built so that the masts fold down. Typically, the most common method is to put some hinges at the very base of the mast into the hull. And the masts will fold back on those hinges. And when they're folded back against the deck, the entire ship is a lot shorter. And it will fit through the bottleneck.

And so you slide the whole ship through the bottleneck and into the bottle, and then you have what's called the forestays. It's the lines that run out from the top of the mast to the bow and then out the bottle. You pull on those forestay lines, and it'll pull the mast back up into position, and then that's the hard part of gluing them down and cutting them off while they're in the bottle. And then the ship's in.

Everything that you've done up to this point is make or break at that moment. And I've had models that I get them to that point and I'm pulling the mass up and something snags or something goes wrong and you got to pull the entire thing out and start over and redo all this rigging.

And yeah, so it is a little bit tense and a little bit exciting because everything is coming together at that point. And when it comes together and everything pulls up correctly, you get all the snags out of the way, it's amazing. Like you just look at it and go, I did this. Yeah.

So now we know how to get a ship into the glass bottle. But some of you might still be asking, why? Why would you want to do this? Sure, it's fun and it's cool to look at. But is there a purpose? Daniel says there is. You always have to ask the question, how did it get in there?

And that's kind of the fun part even for me when I build them and I show them off to people and they just look at them stunned and go, how did that get in there? And then you explain the process. Partly I think especially for sailors back in the day, it provides a good –

protection for these little tiny models. Daniel has built over 50 model ships in the past four years. He says a really simple ship can be built and finished in a couple of hours. More complicated setups can take months. It depends on how detailed you want your ship to be. And he says it's not just something adults can do. Daniel makes ships and bottles with his kids, and he's done workships on it at his local library.

That's it for this episode. Thanks for listening and for sending us your great questions. Thanks this week to Zachary Whitener at the Gulf of Maine Research Institute for checking out the tide pools with me and to Daniel Siemens, the ship in a bottle builder in Colorado. But Why is produced by Melody Beaudet and me, Jane Lindholm, for Vermont Public Radio. We'll be back in two weeks with an all-new episode. Until then, stay curious. From PR.