Sea turtles, captivating ocean inhabitants, often spark curiosity about their respiratory systems. Despite spending nearly their entire lives submerged, these marine animals are air-breathing reptiles equipped with lungs, unlike fish. They must regularly surface to inhale oxygen from the atmosphere. This characteristic shapes their behavior and survival in marine environments.
How Sea Turtles Breathe
Sea turtles breathe air using their lungs. When a sea turtle surfaces, it performs a rapid and efficient gas exchange. They typically execute a single, explosive exhalation followed by a quick, deep inhalation to replenish their oxygen supply. This process occurs through their nostrils, which are always open.
Unlike mammals that use a diaphragm for breathing, sea turtles, with their rigid shells, employ a unique muscular system for ventilation. Muscles lining their shells, extending from the pelvic to shoulder girdles and attached to the plastron, facilitate air movement. When a sea turtle “rocks” its shoulders at the surface, these muscle movements change pressure within the lungs, allowing for effective gas exchange. Their lungs are located directly beneath the carapace and vertebral column, extending significantly along their body length, which allows for substantial oxygen storage.
Underwater Adaptations
Despite their reliance on air, sea turtles exhibit physiological adaptations enabling them to remain submerged for extended periods, sometimes for several hours when resting or sleeping. They can reduce their heart rate, known as bradycardia. When diving, a sea turtle’s heart rate can slow dramatically, from around 20 beats per minute at the surface to as low as 2 to 3 beats per minute, or even one beat every nine minutes during deeper dives. This conserves oxygen by minimizing its demand throughout the body.
Sea turtles also possess high concentrations of hemoglobin in their blood and myoglobin in their muscles, enhancing their capacity to store oxygen. Myoglobin, a protein in muscle tissue, facilitates oxygen transfer to tissues during prolonged dives. During deep dives, their lungs can partially collapse at depths of about 80-160 meters, which helps reduce nitrogen narcosis or decompression sickness upon ascent. They can also tolerate higher levels of carbon dioxide buildup in their bloodstream, delaying the need to surface. When oxygen levels become extremely low, sea turtles can temporarily switch to anaerobic respiration, a process that generates energy without oxygen, though this is a limited mechanism due to the accumulation of lactic acid.
Why Sea Turtles Have Lungs
The presence of lungs in sea turtles links directly to their evolutionary history and biological classification. Sea turtles are reptiles that evolved on land millions of years ago. Their ancestors were terrestrial animals with lungs for breathing atmospheric air. When these ancient reptiles transitioned back to a predominantly aquatic lifestyle, they retained lungs as their primary respiratory organs.
This contrasts with fish, which evolved gills to extract dissolved oxygen from water. Developing gills would necessitate a complete restructuring of a sea turtle’s anatomy and physiology, an evolutionary shift that has not occurred. Despite their aquatic existence, sea turtles maintain the respiratory system inherited from their land-dwelling lineage. They are obligate air-breathers, meaning they must surface to obtain oxygen.