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Why Is The Sea Salty?

Jane Lindholm
This tiny lobster is a few years old. He lost his eyes and claws in an attack, possibly by another lobster..

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 how model ships get in those glass bottles.

Download our learning guides: PDF | Google Slide | Transcript | Ship In Bottle Plans

"Why is the sea salty?" asks 9-year-old Chase of Enfield, New Hampshire. For an answer, we turned to Zach Whitener, a research associate at the Gulf of Maine Research Institute in Portland, Maine.

"The the bottom of the food chain. Every stream and brook eventually gets to the ocean. Not only do things like salt and mud but also your pollution goes to the bottom of the stream. Rainwater is slightly acidic. When it rains, the rain weathers rocks and pulls some of the ions, or elements out of it, different minerals. It's not just salt, but lots of different things. Salt is the most common one. The salt comes from the rocks and it washes into the streams, then the rivers and eventually into the ocean. Since the ocean is the bottom of the line, there's nowhere else for the salt to go and it builds up in concentration."

"It's not just the ocean that's salty. The Great Salt Lake--a famous lake in Utah--it's very salty because there's no outlet. There's no river from the salt lake to the ocean. So all the salts from the rain out west, they go into the salt lake."

Credit Jane Lindholm / VPR
The Gulf of Maine Research Institute's Zach Whitener grew up lobstering. He started researching lobsters when he was a teenager and was inspired to become a scientist.

"How do mussels get their shells?" — Lauren, 6, Washington, NH

Credit Lauren's mom / courtesy
Lauren is in second grade. When she is not asking lots of questions, she likes to do gymnastics, and climb things.

"When mussel eggs first hatch, the larval mussel 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!

As soon as they attach to the bottom, the mussels already have the very beginnings of their shells. Just like when we eat food, we can use the nutrients in our bodies 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 an inner tidal pool with 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 thick shells to protect themselves. However, people have found with mussel farms offshore, when the mussels aren't around predators they put very little energy into producing shells. They still have shells, but they are very brittle. Scientists believe that the mussels can smell their predators. There are chemicals called pheromones, chemicals in the water, which mussels can smell. And if they can't smell any predators, they have no cue to build thick strong shells." 

— Zach Whitener, Gulf of Maine Research Institute.

Listen to the full episode to learn more about lobsters and about anadromous fish, like alewives, that are specially adapted to live in both salt and fresh water. We also get an answer to a question from 7-year-old Nico in Nashville, TN. He wants to know how you get a ship in a bottle. We meet Colorado-based shipin-bottle builder Daniel Siemens for an explanation.

If you're ready to try building your own ship in a bottle, you can find plans here.

Read the full transcript.

Credit Daniel Siemens
A ship in a bottle built by Colorado artist Daniel Siemens.


Melody is the Contributing Editor for But Why: A Podcast For Curious Kids and the co-author of two But Why books with Jane Lindholm.
Jane Lindholm is the host, executive producer and creator of But Why: A Podcast For Curious Kids. In addition to her work on our international kids show, she produces special projects for Vermont Public. Until March 2021, she was host and editor of the award-winning Vermont Public program Vermont Edition.
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