How to Stay Alive without Oxygen: Marine Mammals, Diving, and COVID-19

The unique diving ability of marine mammals may give researchers a clue into the damaging effects of COVID-19 on humans.

Williams, T.M. & Davis, R.W. (2020). Physiological resiliency in diving mammals: Insights on hypoxia protection using the Krogh principle to understand COVID-19 symptomsComparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2021, 253, 110849.

Amidst a pandemic…

The gracefulness of a humpback whale dive does not reveal how many physiological processes are taking place. (Image Source: Wikimedia Commons, National Marine Sanctuaries)

Coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), changed life as we know it. Upon seeing the list of patient respiratory symptoms, physicians and scientists hurried to understand how coronavirus deprived patients of the oxygen they needed to survive. The deoxygenating effects of COVID-19 even had marine biologists wondering why humans were so susceptible to oxygen depletion, when marine mammals could safely withstand long periods of deoxygenation.

Marine mammals (such as whales, seals, and dolphins) perform incredible feats underwater- all while holding their breath. They lack gills like fish do, so they must breathe air at the surface and hold breath while diving or foraging for food. In 2014, the Curvier beaked whale broke all marine mammal breath-holding records when it survived on one breath for 2 hours and 17 minutes!

Diving deeper with marine mammals

Since marine mammals spend most or all of their lives at sea, they have developed a unique way to hold their breath while diving that allows them to tolerate both high and low oxygen environments while remaining healthy overall. The diving response involves a series of abrupt, physiological changes to the animal’s organs.

A human free-diver swimming close to a sperm whale underwater in Azores. (Image Source: Wikimedia Commons, Will Falcon aka Vitaly Sokol)

After taking a breath at the surface of the water, the animal becomes apneic (stops breathing) for the remainder of the dive. Their bodies cycle through the stages as they go from the surface to submerging. First, they exhale and collapse their lungs, reducing buoyancy, making them dive deeper and also able to withstand the pressure underwater. While diving, they lower their heart rate to conserve the oxygen remaining in their lungs. Finally, by constricting and relaxing blood vessels, they shunt blood to the tissues with higher oxygen needs- the brain, heart, and muscles.

Wild marine mammals may undergo these physiological cycles over 100 times each day while they dive and forage! Ultimately, their body’s cycle between oxygen depletion and oxygen restoration each day. So how do they remain healthy and thriving?

Scientist found specific adaptations that humans did not possess. For example, the blood of marine mammals has a higher carrying capacity for oxygen than humans. Some species, like Weddell seals, contract their spleens during a deep dive to increase the amount of oxygen-rich blood into circulation. Another safety feature found was the presence of antioxidants, which make the tissues of marine mammals easier to be filled with oxygenated blood (re-perfusion) and recover after a dive.

How do marine mammals compare to COVID-19 patients?

When marine mammals dive, oxygen levels in their blood decrease by 40 – 50% of the values of oxygen on the surface. Humans are usually given oxygen if their oxygen saturation level decreases by just 10%. When humans have a 20% decrease in their blood oxygen saturation, they are hypoxic (oxygen deprivation) and organ function is already compromised. An even further drop of oxygen in humans would lead to respiratory or cardiac arrest, unconsciousness, or death.

Some species of seal contract their spleens during a deep dive to increase the amount of oxygenated blood. (Image Source: Wikimedia Commons, Wordless symbol)

A diving marine mammal has oxygen levels which mimic those of humans in a COVID-19-induced deoxygenated state. However, marine mammals are resistant to these effects during low oxygen periods and are able to continue to actively live their lives (hunt, swim, play) in these types of environments.

This is the result of 50 million years of evolution that has allowed marine mammals to develop mechanisms to protect their organs underwater: Marine mammals descend from a line of terrestrial ancestors that re-entered the oceans and evolved ways to safeguard their oxygen-sensitive tissues in low oxygen environments. In contrast, human oxygen-sensitive tissues are quickly damaged by lack of oxygen, as seen in COVID-19 patients. Humans sustain rapid and irreversible damage to heart, brain, and lung tissue after just minutes in a low oxygen environment. In view of this, it is not surprising why many recovered COVID-19 patients have difficulty recovering to their previous function. Unfortunately, we cannot turn into dolphins to protect our bodies from COVID-19, but looking at nature helps us understand the limits of the human body and how vulnerable we really are.

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