Aquatic Turtles: Staying Underwater, How?

Turtles are fascinating creatures, and while they are primarily land-based, they are extremely well-adapted to aquatic environments. Despite needing to breathe air, turtles can stay underwater for long periods, and some species have even learned to extract oxygen from the water itself. This ability to remain submerged is due to their slow metabolisms, which fluctuate with temperature, and their unique breathing techniques. So, how do aquatic turtles manage this impressive feat of staying underwater for so long?

Slowing metabolism and heart rate

Aquatic turtles are well-equipped to stay underwater for long periods. While they cannot breathe underwater, they have the ability to hold their breath for far longer than humans.

The length of time a turtle can stay underwater depends on its species, location, and the temperature of the water. For example, the Fitzroy River turtle of Australia hardly ever surfaces, instead obtaining oxygen from water pumped through its cloaca, or posterior opening. This is likely an adaptation to limit its exposure to crocodiles.

During the day, in warm water, turtles breathe regularly. However, at night, their metabolism slows down, and they can stay underwater for several hours at a time. Aquatic turtles can stay underwater for up to seven hours while they sleep. After they wake up, their metabolism and heart rate speed up, and they need to surface to breathe more often.

Some turtles, such as the slider (Trachemys scripta) and the painted turtle (Chrysemys picta), have particularly slow metabolisms. This enables them to stay underwater for extended periods. These turtles have also adapted to extract oxygen from the water, allowing them to remain underwater for an entire winter.

Turtles are ectothermic, or "cold-blooded," which means they warm their bodies using external sources such as sunlight and warm water. As a result, their metabolic rate fluctuates with the temperature. When the temperature is warm, a turtle's metabolism is faster, and it requires more oxygen. Conversely, when the temperature is cool, a turtle's metabolism slows down, reducing its oxygen needs.

During hibernation, turtles can slow their metabolism and reduce their need for oxygen. Some turtles, such as snapping turtles (Chelydra serpentina) and painted turtles, can survive in low-oxygen waters by using anaerobic metabolism and active chemical buffering processes.

Absorbing oxygen through the throat

Aquatic turtles have a variety of adaptations that allow them to stay underwater for extended periods of time. One of these adaptations is the ability to absorb oxygen through their throats.

While turtles are primarily land creatures, they are well-equipped for aquatic life. They have three different ways of breathing: through their lungs, which is their primary means of respiration; through their mouths and throats, especially when underwater; and through their cloaca, or posterior opening, when hibernating.

The process of absorbing oxygen through the mouth and throat involves pumping water into these cavities, then extracting the oxygen from the water. This is achieved by pumping water in through the nose and mouth, and absorbing the oxygen using the surface of the throat and mouth. This method of respiration is not the same as breathing through lungs, as turtles are not pumping air into their lungs. Instead, they are absorbing oxygen directly from the water.

This method of respiration is particularly useful for aquatic turtles, as it allows them to stay underwater for longer periods of time. By absorbing oxygen through their throats, aquatic turtles can stay submerged for several hours at a time, especially while sleeping. During sleep, some species will use this form of respiration, while others rely on oxygen storage and a slower metabolism and heart rate, which reduces their overall oxygen needs.

The ability to absorb oxygen through the throat is just one of the ways that turtles have adapted to aquatic life. Their slow metabolisms also play a role in their ability to stay underwater for extended periods. For example, the painted turtle (Chrysemys picta) and the slider (Trachemys scripta) have slow metabolisms, which means they require less oxygen and can stay submerged for longer. Additionally, some aquatic turtles from northern areas will hibernate underwater during the winter, burying themselves in the substrate of a lake or river bottom. During hibernation, their metabolic rate drops significantly, further reducing their need for oxygen.

Absorbing oxygen through the cloaca

The cloaca, or the butt, is an essential part of a turtle's anatomy that enables it to stay underwater for extended periods. This process, known as cloacal respiration, involves the diffusion of oxygen into the body and carbon dioxide out of the body through the cloaca. While it is not considered true breathing, it serves as an alternative respiration mechanism in hypoxic environments, supplementing the blood oxygen levels.

Cloacal respiration is particularly useful for turtles during hibernation or brumation in the winter months. As cold-blooded animals, turtles experience a drop in body temperature and a subsequent slowdown in metabolism during winter. This reduced metabolic rate lowers their oxygen requirements, and the oxygen diffused from the water flowing over their bodies is sufficient to sustain them. The Fitzroy River turtle (Rheodytes leukops) from Australia is exceptional in this regard, deriving about 70% of its energy through cloacal respiration, enabling it to stay underwater for up to three weeks.

The cloaca is a posterior opening with a rich supply of blood vessels, making it an efficient site for gas exchange. Some turtles have a pair of accessory air bladders connected to the cloaca, enhancing their ability to absorb oxygen from the water. This adaptation is especially advantageous for turtles living in fast-flowing rivers or those that brumate in frozen ponds, as it allows them to extend their time underwater and avoid predators.

Cloacal respiration is not as efficient as lung breathing due to the lower oxygen content in water compared to air. However, it serves as a vital secondary mechanism for turtles to survive in challenging environments. During brumation, when turtles cannot breathe normally, cloacal respiration becomes their primary means of obtaining oxygen, allowing them to remain submerged for extended periods.

While cloacal respiration is essential for turtles, it is not their only adaptation for staying underwater. Aquatic turtles have slow metabolisms and can extract oxygen from the water through specialised structures in the throat and cloaca. Additionally, they can slow down their metabolism and heart rate, further reducing their oxygen requirements. These adaptations enable aquatic turtles to stay underwater for several hours, especially during sleep.

Anaerobic metabolism

During anaerobiosis, or oxygen deprivation, the freshwater turtle Pseudemys scripta elegans provides an excellent example of anaerobic metabolism in action. Its body undergoes several changes to adapt to the lack of oxygen. Firstly, there is a decrease in liver glycogen and a corresponding increase in blood glucose levels. Cardiac glycogen, which provides energy for the heart, is depleted within three hours, highlighting the importance of an efficient energy source during anaerobiosis.

The rate of glycolysis, a process that generates energy in the absence of oxygen, increases during the initial six hours and then gradually decreases. This indicates that glycolysis plays a crucial role in energy production during the early stages of oxygen deprivation. However, the inefficiency of glycolysis limits the turtle's survival during prolonged anaerobiosis.

Additionally, the turtle's ATP (adenosine triphosphate) and creatine phosphate stores, which are essential for energy transfer and muscle function, begin to deplete within the first three hours and are almost entirely exhausted after 15 hours. This depletion further contributes to the limitations of anaerobic survival.

The metabolic rate of turtles is relatively low compared to warm-blooded animals, and it fluctuates with temperature. When temperatures are cool, a turtle's metabolism slows down, reducing its oxygen requirements. This adaptation allows some turtles to hibernate underwater for extended periods, surviving on minimal oxygen absorbed directly from the water.

In conclusion, anaerobic metabolism in turtles involves a series of physiological changes that enable them to cope with oxygen deprivation. While these adaptations allow turtles to survive in low-oxygen environments, they are not indefinitely sustainable due to the inefficiency of anaerobic energy production. Therefore, turtles must eventually return to the surface to breathe, especially when their body temperatures rise and their metabolic rate increases.

Access to oxygenated water

Aquatic turtles can remain underwater for extended periods due to their ability to access oxygenated water. While turtles cannot breathe underwater, some species have evolved to absorb oxygen while submerged, allowing them to stay underwater longer than other land animals. This is achieved through specialised structures in the throat and cloaca, also known as the posterior opening or butthole.

The cloacal respiration method is not exactly breathing; it involves diffusing oxygen into the body and releasing carbon dioxide through the cloaca. This process is less efficient than lung breathing as water contains approximately 200 times less oxygen than air. However, it enables turtles to survive in fast-moving rivers and avoid predators. The Fitzroy River turtle, native to Australia, derives about 70% of its energy through cloacal respiration, allowing it to stay underwater for up to three weeks.

During hibernation, aquatic turtles from northern regions may bury themselves at the bottom of lakes or rivers, reducing their metabolic rate and oxygen requirements. They can absorb the necessary oxygen directly from the water, allowing them to hibernate underwater for several months. This adaptation is particularly advantageous in extremely cold lakes, where oxygen levels can drop dangerously low.

The ability to utilise oxygenated water enables aquatic turtles to stay submerged for hours while sleeping. During sleep, some species rely on cloacal respiration, while others depend on oxygen storage and a slower metabolic rate and heart rate, reducing their oxygen requirements. As a result, aquatic turtles can remain underwater for up to seven hours while asleep.

In summary, aquatic turtles have evolved unique adaptations to access oxygenated water, allowing them to stay underwater for extended periods. This ability varies across species, with factors such as locality and temperature influencing the duration they can remain submerged.

Frequently asked questions