Sea turtles are marine reptiles that spend most of their lives in the ocean. Despite their aquatic existence, they are air-breathers, possessing lungs and needing to surface regularly for oxygen. This presents a challenge, as they must balance underwater activities with periodic trips to the surface. Their ability to thrive in both environments shows biological adaptations.
The Mechanics of Sea Turtle Respiration
Sea turtles breathe air using lungs. Their respiratory system is adapted for rapid and efficient gas exchange when they surface. Unlike mammals, sea turtles cannot expand their rib cages due to their rigid shells. Instead, they rely on muscular contractions to facilitate breathing.
Breathing involves movements of muscles attached to their pelvic and shoulder girdles, as well as their plastron. These muscles alter the pressure within their body cavity, allowing air to be drawn into and expelled from their lungs. Their lungs extend along much of their body, allowing them to take in a substantial volume of air.
When a sea turtle surfaces, it extends its head and uses its nostrils to inhale and exhale quickly. The glottis closes tightly underwater to prevent water from entering the respiratory tract. This specialized breathing mechanism allows them to exchange gases efficiently during brief surface intervals before submerging again.
Underwater Endurance and Oxygen Conservation
Sea turtles possess physiological adaptations that enable them to remain submerged for extended periods. While active, they typically dive for 20 to 40 minutes, but when resting or sleeping, they can hold their breath for several hours. Some species, like green sea turtles, can stay underwater for 5 hours. In colder water, their breath-holding capacity can increase further, with some loggerhead turtles recorded submerged for seven hours during overwintering.
One adaptation is a significantly reduced metabolic rate. Being cold-blooded, their metabolic rates are naturally lower than those of warm-blooded animals, reducing their oxygen consumption. This allows them to use oxygen more slowly, conserving their stored supply. During dives, sea turtles also exhibit a “diving reflex” that includes bradycardia, a slowing of their heart rate. Their heart rate can decrease significantly, sometimes to as low as one beat every nine minutes.
Sea turtles can selectively shunt blood flow away from less oxygen-sensitive organs and tissues towards the brain, heart, and central nervous system, ensuring these areas receive a continuous oxygen supply. They store large amounts of oxygen in their blood and muscles. High concentrations of hemoglobin in their blood carries oxygen, and myoglobin in their muscles stores it. Sea turtles also have a higher tolerance for carbon dioxide buildup in their blood compared to many other vertebrates, which delays the urge to surface for a breath. These combined adaptations allow sea turtles to maximize their underwater time for foraging, resting, and migration.