with a series of videos about the oceans.

We're not just talking about creatures with gills, though,

we're also talking about air-breathing animals that have adapted to living and hunting in the ocean

because they are really good at holding their breath.

Sperm Whales and Elephant Seals can stay underwater for an hour or two

which is pretty impressive for marine mammals

And the Cuvier's Beaked Whale holds the mammalian title for

longest recorded dive at 137 and a half minutes

So what is going on in their bodies that make these long dives possible?

We need oxygen to help our cells make energy,

in a process that also makes carbon dioxide.

When you have too much carbon dioxide in your body,

it makes your blood more acidic

which signals your brain to say "Hey, you need to get oxygen! Breathe now!"

So when an animal like a human or whale breathes,

the oxygen molecules in the air diffuse from the lungs into tiny blood vessels

and bind to a protein inside your red blood cells called hemoglobin.

Hemoglobin acts as a delivery truck in your body

using the bloodstream as its highway to hand-off oxygen molecules to tissue cells

or another protein called myoglobin in muscle cells.

Myoglobin is basically extra oxygen storage for your muscles, because they need extra energy when they're active

And scientists think that myoglobin is what helps marine mammals hold their breath for so long.

For one thing:

These diving animals have more hemoglobin and myoglobin than humans,

which means they can store more oxygen in their blood and muscles.

When the oxygen bound to hemoglobin in their blood runs out,

the myoglobin can release extra 02 back into the bloodstream.

Plus, we think aquatic mammals have a higher tolerance to dissolved carbon dioxide in their blood,

so there might be a less urgent 'need-to-breathe' instinct.

And when the animal resurfaces to breathe and prep for another dive,

the excess carbon dioxide dissolved in the blood and bound to hemoglobin is released and replaced with fresh oxygen.

A 2013 study also found that these:

specifically the ones that live on land.

Too many myoglobin molecules tend to clump up together in the muscles,

and in humans this can cause diseases.

But if those molecules have strong asimilar surface charges, they repel each other instead.

This means all the extra myoglobin molecules are free to store oxygen and help the animals stay underwater longer.

And some animals have other oxygen-saving adaptations as well,

like a lower heart rate, and restricted blood supply to tissues.

Scientists are still trying to find even more adaptations

and understand how they work together in different species to conserve oxygen during these long, deep dives.

But if you're waiting for the day when humans can stay underwater for hours without equipment,

don't hold your breath!

[laughing]

Thank you for asking, and thank you especially to Ecology Project International for sponsoring this episode.

EPI is an international non-profit organization that works to improve and inspire science education and conservation efforts

through student-scientist partnerships.

EPI has recently become the steward of the Pacuare Nature Reserve in Costa Rica,

which is home to 5% of the world's biodiversity and the 4th most important nesting beach for vulnerable leatherback sea turtles.

To sustain the reserve and its majestic wildlife long into the future,

EPI has launched an online fundraising campaign.

You can help protect the thousands of species of flora and fauna that call Pacuare home

Check out EPI's fundraising campaign at crowdrise.com/PreserveProtectPacuare