If you ever have the opportunity to see an elephant seal sneeze, you’ll probably notice something a little unusual. Around their nostrils is a bright white discharge. It’s so white, it’s almost like they’re sneezing paint.
But that’s not just “seal snot.” It’s actually the remarkable substance that makes it possible for elephant seals to survive dives that exceed the estimated collapse-depth of a Seawolf-class nuclear submarine.
Elephant seals are among the planet’s most accomplished free-divers. They routinely make journeys to depths between 300 to 900 meters (1,000 to 3,000 feet) with one particularly deep recorded dive reaching an astounding 2,388 meters. That’s more than 1.5 miles underwater!
Even more impressive is that fact that they can stay down there in the crushing depths for periods of up to 100 minutes (though the average is 20 minutes), surfacing only for a few minutes between their excursions back into the abyss.
These vertical back and forth rhythms can go on for hours during their months-long excursions away from land and, in the process, they subject their bodies to enormous pressure differentials.
The ambient pressure increases by 1 atm every 10 meters underwater. That means that at depths of around 900 meters, elephant seals experience the rough equivalent of 90 atmospheres worth of pressure bearing down on every point on the surface of their body. The ocean wants to crush them like an empty aluminum can and, remarkably, the elephant seals survive.
Part of that survival ability is due to that amazing white pulmonary surfactant seen around their nostrils when the seals are on the surface. Pulmonary surfactants are vital to the ability of mammals, including humans, to breath. We need surfactants to lower the surface tension of the fluid coating our lungs which, in turn, allows the tiny alveoli to function as an conduit for oxygen and carbon dioxide traveling between our lungs and blood. Without it, we’d suffocate. We’d essentially drown in our own lung fluid.
In elephant seals, this surfactant also serves a secondary function. When an elephant seal makes an extremely deep dive, its lungs collapse under the immense pressure. Their respiratory tissues all begin to compress and the alveoli are smashed together into a tighter and tighter space as the seal’s lungs buckle and fold. When the animal heads back to the surface, that process reverses and its the unique white-colored surfactant that makes that rapid, seemingly effortless re-expansion possible.
Studies of elephant seal surfactant have shown that, aside from the normal surface-tension lowering functions found in other mammals, it acts as an anti-adhesive. It prevents lung tissues from sticking together and allows the seal’s lungs to go through frequent cycles of rapid collapse and re-expansion as though nothing happened. Non-stick lungs! I can already hear the infomercial, “Order now, and get an extra 100 meters of depth and 10 minutes of dive time free!”
By studying the properties of these surfactants (with their unique composition that features greater concentrations of short-chain phospholipids, more fluidic species of phosphatidylcholine, a relative decrease in anionic phospholipids, and a decrease in surfactant protein B compared to terrestrial mammals), researchers may be able to help improve the artificial surfactants used to treat human patients like premature infants who suffer from inadequate surfactants or patients whose surfactants have been affected by trauma.
For the seals, however, it’s just business as usual.
References and Further Reading:
Castellini, M.A., Mellish, J.A. (2015). Marine Mammal Physiology: Requisites for Ocean Living. CRC Press.
Miller, N. J., Daniels, C. B., Schürch, S., Schoel, W. M., & Orgeig, S. (2006). The surface activity of pulmonary surfactant from diving mammals. Respiratory physiology & neurobiology, 150(2), 220-232.
Ponganis, P. J. (2015). Diving physiology of marine mammals and seabirds. Cambridge University Press.
Robinson, P. W., Costa, D. P., Crocker, D. E., Gallo-Reynoso, J. P., Champagne, C. D., Fowler, M. A., … & Kuhn, C. E. (2012). Foraging behavior and success of a mesopelagic predator in the northeast Pacific Ocean: insights from a data-rich species, the northern elephant seal. PloS one, 7(5), e36728.
Rugonyi, S., Biswas, S. C., & Hall, S. B. (2008). The biophysical function of pulmonary surfactant. Respiratory physiology & neurobiology, 163(1), 244-255.
Spragg, R. G., Ponganis, P. J., Marsh, J. J., Rau, G. A., & Bernhard, W. (2004). Surfactant from diving aquatic mammals. Journal of Applied Physiology, 96(5), 1626-1632.
Ponganis, P. J. (2011). Diving mammals. Comprehensive Physiology.
UC Santa Cruz News Center – Elephant seal tracking reveals hidden lives of deep-diving animals