Sea otters are known for floating on their backs while eating, grooming, and even sleeping. Their ability to spend so much time in the water often leads people to wonder – can sea otters actually breathe underwater?
If you’re short on time, here’s a quick answer to your question: Yes, sea otters can breathe underwater. They have adaptations like closing nostrils, slowing heart rate, and high blood oxygen storage that allow them to hold their breath for up to 5 minutes.
In this article, we’ll take a deep dive into sea otter physiology to understand how they are able to stay submerged for so long. We’ll look at their nostrils, heart rate, blood and lung adaptations, and dive response that enables their underwater breathing feats.
Sea Otter Nostrils Close When Submerged
Nose Closure Keeps Water Out
When sea otters dive below the water’s surface to forage for food, their nostrils have an amazing ability to close tightly to prevent water from entering (Monterey Bay Aquarium). This crucial evolutionary adaptation allows sea otters to hunt for shellfish, crabs, sea urchins, and other prey on the seafloor without drowning.
According to marine biologists, sea otters have special muscles surrounding their nostrils that constrict automatically when they submerge. The nostrils squeeze together tightly, forming a waterproof seal to block water entry.
This keeps their sensitive nasal passages safe while diving up to 300 feet deep in search of snacks.
Research shows adult sea otters can hold their breath underwater for an astounding 5-8 minutes while hunting before they must come back up to the surface for air. Their nose closure trick is part of what makes such deep, lengthy dives possible without injury.
Reopening Nostrils After Surfacing
Sea otter nostrils do not stay closed forever, of course. They are designed to reopen automatically when the animal surfaces from a dive, allowing air entry again so they can breathe (World Wildlife Fund).
Scientists believe specialized oxygen-sensing receptors in sea otters’ bodies detect when they re-enter the air and signal the nasal muscles to relax. This opens the nostrils back up almost instantly. It only takes nanoseconds for the nostrils to regain function after each dive.
If sea otters could not reopen their noses to breathe air after time underwater, they would quickly suffer oxygen starvation and drown because they are still mammals dependent on air like all other mammals.
Their unique nose muscles ensure they get air when needed while also staying watertight when necessary for diving to impressive depths in search of their next snack.
Slowed Heart Rate Conserves Oxygen
Bradycardia Allows Long Dives
Sea otters have adapted the amazing ability to slow their heart rate in order to conserve oxygen while diving underwater for up to 5 minutes. This process, known as bradycardia, allows sea otters to reduce their heart rate to about 10 beats per minute during a dive, compared to around 100 beats per minute while resting at the surface.
By dramatically slowing their heart, sea otters are able to conserve oxygen when they are separated from atmospheric oxygen for many minutes at a time. The lowered heart rate causes blood to flow more slowly through the body, requiring less oxygen to sustain basic physiological functioning.
Research has found that the length of sea otter dives was directly linked to lowering their heart rate – the more they reduced their heartbeat, the longer they were able to remain underwater without needing to breathe.
This suggests that bradycardia allows sea otters to survive the low oxygen conditions of diving below the ocean’s surface for as long as possible before resurfacing to gulp more air.
Heart Rate Increase After Surfacing
While sea otters can survive with extremely low heart rates during dives, their bodies cannot sustain such slow circulation at the surface. When sea otters resurface from a dive, their heart rate rapidly accelerates to send oxygenated blood around the body.
Researchers have recorded heart rates of around 300 beats per minute in sea otters immediately after long dives. This represents a whopping 30x increase from the slow heart rate during time underwater!
Their heart steadily returns to a normal resting rate over the next few minutes as they breathe at the surface.
By slowing their heart to the bare minimum needed during dives, sea otters are able to conserve precious oxygen. In contrast, immediately after surfacing they rapidly increase their heart rate to quickly deliver oxygen and regain normal body functioning.
This unique “switching” between bradycardia and tachycardia allows sea otters to successfully dive and forage underwater for food while surviving low oxygen conditions.
High Blood Oxygen Storage
Hemoglobin and Myoglobin Stores
Sea otters have exceptionally high levels of hemoglobin and myoglobin in their blood and muscles, allowing them to store large amounts of oxygen when they are at the surface. Hemoglobin is the protein in red blood cells that carries oxygen, while myoglobin is a similar protein found in muscles that also binds oxygen.
Sea otters have hemoglobin levels 2-3 times higher than terrestrial mammals of similar size, and myoglobin levels nearly 10 times higher.
| Animal | Hemoglobin Level (g/dL) | Myoglobin Level (mg/g) |
|---|---|---|
| Sea otter | 20-25 | 10-14 |
| Terrestrial mammal (average) | 12-15 | 2-4 |
This allows sea otters to load up on oxygen when breathing at the surface, providing an oxygen supply to last through extended dives underwater where they cannot breathe. The high hemoglobin and myoglobin concentrations are an important evolutionary adaptation that enables the sea otter’s fully aquatic lifestyle.
Quick Oxygenation During Surface Breaths
In addition to having increased oxygen storage capacity, sea otters are excellent at rapidly replenishing these stores each time they return to the surface to breathe. They have large lungs for their body size and take very fast, deep breaths at the surface.
Their specialized lungs have reinforced airway cartilages that maintain open airways during these rapid breathing cycles.
Sea otters can replace 90% of the oxygen in their lungs with each breath at the surface, compared to only 15-20% replacement in humans and other terrestrial mammals. This efficient oxygen loading allows them to optimize their oxygen stores in just a few breaths before diving again.
Together with their enhanced hemoglobin and myoglobin concentrations, this physiological adaptation grants sea otters the ability to hold their breath for up to 5-8 minutes during dives – much longer than terrestrial mammals of similar size could endure underwater.
Their high blood oxygen storage and rapid oxygenation abilities are crucial to their success as marine foragers.
Lung Collapsing Aids Buoyancy
One Lung Remains Inflated
Sea otters have the incredible ability to collapse one of their lungs while diving underwater. This helps them control their buoyancy and stay submerged for longer periods to hunt for food. When sea otters dive, they are able to deflate one lung, while keeping the other lung inflated at about 2/3 its normal size.
The inflated lung provides enough oxygen, while the collapsed lung prevents unnecessary buoyancy that could cause them to float back up.
Researchers have found that sea otters can remain submerged for over 5 minutes while hunting by utilizing this lung collapsing technique. The muscular diaphragm surrounding the lungs allows them to voluntarily collapse one lung when needed.
In fact, sea otters have the greatest lung capacity for their size among marine mammals. This helps make them perfectly adapted for their aquatic lifestyle of diving for shellfish on the seafloor.
Reinflation After Surfacing
After sea otters have finished their hunting dive and resurfaced, they need to reinflate their collapsed lung. Sea otters have complete control over the inflation and deflation of their lungs. To reinflate, they simply breathe in air which opens up the alveoli air sacs in the collapsed lung once again.
This reinflation happens quickly after surfacing, allowing for efficient cyclic dives.
The sea otter’s muscular diaphragm also aids the reinflation process. The diaphragm pulls down to fully expand the lungs with each breath. Within a few breaths at the surface, the collapsed lung is reinflated and oxygen levels are restored.
This unique lung collapsing ability allows sea otters to make excellent use of their aquatic environment, without wasting energy fighting buoyancy. Their specialized lungs are one of the many adaptations that make sea otters such accomplished marine foragers.
Efficient Dive Response Activation
Triggered by Cold Water
Sea otters have an astounding ability to slow their heart rate and reduce blood flow when diving underwater, allowing them to hold their breath for up to 5 minutes to hunt for food along the seafloor (this efficient physiological adaptation is known as the “dive response”).
This beneficial reaction is automatically triggered when a sea otter’s face makes contact with cold ocean water.
Researchers have found that immersion in water less than 68°F (20°C) causes sea otters’ metabolic rates to plunge, with heart rates dropping from normal levels over 100 beats per minute down to just 10 beats per minute.
Blood flow is also restricted from the otters’ extremities and outer layers of skin, allowing core body parts like the heart and brain to function with less oxygen.
Blood Flow Reduction
Interestingly, sea otter pups have to learn how to intentionally elicit this efficient physiological reaction when they dive. Adult otters teach the pups by repeatedly pushing them underwater, conditioning them to instantly activate oxygen conservation mechanisms when submerged.
Research by the Monterey Bay Aquarium found that by 10 weeks old, sea otter pups can reduce their heart rates by 30% underwater. This ability continues to improve with practice until the otters master holding their breath by 4 months old.
So in just a matter of months, sea otter pups go from barely dipping below the surface to diving 150 feet underwater in search of sea urchins, crabs, and more! Their extremely efficient dive response activation allows these exceptional marine mammals to take on the chilly Pacific Ocean in pursuit of their next snack.
Conclusion
In summary, sea otters have a number of specialized adaptations that allow them to breathe underwater. The closure of their nostrils, dramatic slowing of their heart rate, high blood oxygen storage capacity, collapsible lungs, and extreme dive response all enable sea otters to hold their breath at depth for up to 5 minutes.
So next time you see a sea otter floating at the ocean’s surface, know that it has some incredible physiology going on beneath the waves that allows it to dive and breathe efficiently underwater.
