(Intro)

We're celebrating Earth's oceans this week 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 a hundred and thirty-seven 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 O₂ 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 breath instinct. And when the animal resurfaces to breath 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 expert mammalian diver have more positive charge on the surface of their myoglobin molecules compared to other mammals, 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 similar 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. (Laughs)

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 five percent of the world's biodiversity and the forth 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.