Seals may be able to directly sense oxygen levels in their blood, an ability humans don't possess. A Scottish study reveals these marine mammals adjust their dives based on this vital parameter.
Unlike land animals, which primarily rely on CO₂ levels to trigger breathing, seals appear capable of "feeling" their blood oxygenation. This discovery, published in
Science, sheds light on the mechanisms allowing them to avoid drowning during prolonged dives.
An ingenious experiment to solve the mystery
Grey seals were placed in a pool equipped with a breathing chamber and fish dispenser. Researchers modified the air composition in the chamber, varying oxygen and CO₂ levels. The animals dove freely to feed, allowing observation of their behavior.
When oxygen was more concentrated, seals extended their dives. Conversely, oxygen-depleted air made them surface faster. CO₂, however, didn't influence their dive duration. These results suggest direct sensitivity to oxygen, not CO₂.
This ability would allow seals to adjust their effort based on their reserves. Unlike humans, who risk fainting during apnea, they thus avoid exhausting their reserves before resurfacing.
An adaptation for marine life
Land mammals, including humans, don't directly perceive their blood oxygen levels. Their breathing is triggered by CO₂ accumulation, an effective mechanism in air but risky when diving. Seals appear to have developed heightened oxygen sensitivity.
This peculiarity might explain why grey seals can dive up to 2,000 feet (600 meters) without losing consciousness. Their ability to "monitor" oxygen would allow them to surface before reaching critical thresholds.
Similar studies on other marine species (turtles, crocodiles) suggest this trait might be shared. Future research could determine whether this adaptation is common to all diving mammals.
Article author: Cédric DEPOND