Turtles primarily breathe air using lungs. While all turtles must surface for oxygen, some aquatic species have unique adaptations to absorb oxygen from water, allowing longer underwater periods. This combination of air breathing and aquatic respiration enables them to thrive in diverse environments.
Breathing Air: The Primary Method
All turtles rely on lungs for respiration. Air enters through their nostrils, travels down the trachea, and into their spongy lungs. Unlike mammals, turtles cannot expand their rib cages due to their rigid shells. Instead, they use a unique muscular system to change internal pressure, creating a bellows-like action to draw air in and push it out.
Some tortoises use rhythmic throat movements, known as gular pumping, to move air. The glottis, located at the back of the tongue, directs airflow, opening for air and closing during dives to prevent water entry.
Breathing Water: Specialized Aquatic Respiration
While lungs are primary, some aquatic turtles absorb oxygen from water. One notable method is cloacal respiration, often called “butt breathing.” This involves specialized, vascularized sacs, called bursae, within the cloaca—a multipurpose opening at the base of the tail.
These turtles pump water in and out of their cloaca, allowing dissolved oxygen to diffuse across the blood vessels in the bursae into their bloodstream. The Fitzroy River turtle (Rheodytes leukops) is a prominent example. Another form is pharyngeal respiration, where vascularized tissues in the throat and mouth, lined with small projections called villi, absorb oxygen from water pumped over them. These aquatic breathing methods enable extended underwater stays, especially during periods of low activity or brumation.
Adaptations to Diverse Habitats
Different turtle species exhibit varied respiratory strategies tailored to their environments. Terrestrial tortoises, living exclusively on land, rely solely on air breathing through their lungs. They are not adapted for prolonged submersion and can only hold their breath for a limited time, typically 20 to 30 minutes.
Semi-aquatic freshwater turtles, while primarily air-breathers, often use cloacal or pharyngeal respiration to prolong underwater time. This allows them to forage or remain concealed longer, but they must still regularly surface for air. Marine sea turtles, highly adapted for oceanic life, also exclusively breathe air using their large, efficient lungs. They can hold their breath for extended durations, from 20 to 40 minutes during foraging dives to several hours when resting, due to adaptations like slowing their heart rate and metabolic rate.
Environmental Influences on Respiration
External environmental factors significantly impact a turtle’s respiratory patterns and ability to remain submerged. Water temperature plays a role; in colder water, a turtle’s metabolic rate decreases, reducing oxygen demand and allowing for longer dives or extended underwater periods during brumation. Some species can even survive for months under ice by relying on reduced metabolic needs and aquatic respiration.
Water quality, specifically oxygen levels, also affects breathing. If oxygen levels in the water are low, turtles are forced to surface more frequently for air. Prolonged submersion without access to air, such as entanglement in fishing nets, can lead to drowning, even for highly aquatic species. Similarly, aquatic turtles exposed to prolonged periods out of water can face dehydration and respiratory issues, highlighting the delicate balance between their adaptations and environmental conditions.