Many people wonder if turtles can breathe underwater like fish. While highly adapted to aquatic life, turtles are reptiles with lungs, meaning they cannot extract oxygen directly from water like fish do with gills. Their ability to remain submerged for extended periods involves specialized respiratory adaptations and physiological adjustments. This article explores how turtles obtain oxygen, both from the air and, in some cases, from water.
Air Breathing in Turtles
Turtles primarily rely on lungs for respiration and must surface to breathe air. Their lungs, located beneath the carapace, are spongy and designed for gas exchange with the atmosphere. Unlike mammals, turtles do not possess a diaphragm to facilitate breathing.
Instead, they use a muscle system to inflate and deflate their lungs. Sheets of muscles within their shell contract and relax, altering pressure in the peritoneal cavity, forcing air in and out. Additionally, some species can use movements of their limbs, specifically the shoulder and pelvic girdles, to change pressure and assist ventilation.
Underwater Oxygen Absorption
Although turtles cannot “breathe” water like fish, some species have developed supplementary mechanisms to absorb oxygen from their aquatic environment. These methods are crucial for extending their time underwater, particularly during periods of inactivity or when surfacing is not possible. These adaptations complement lung breathing rather than replacing it.
One of the most well-known adaptations is cloacal respiration, sometimes informally called “butt breathing.” Certain freshwater turtles, such as Australian freshwater turtles, possess specialized sac-like structures called bursae within their cloaca. These bursae are richly lined with tiny, finger-like projections (papillae) that are highly vascularized. Turtles can actively pump water in and out of the cloaca, moving it over these vascularized tissues to allow dissolved oxygen to diffuse into their bloodstream. This mechanism is particularly important during brumation, when turtles may spend months submerged in cold water where oxygen needs are significantly reduced.
Another adaptation is buccopharyngeal respiration, where some turtles absorb oxygen through the vascularized lining of their mouth or throat. They achieve this by rhythmically pumping water over these tissues, a process sometimes referred to as buccal pumping. While this can contribute to oxygen uptake, it is less efficient than lung respiration.
Some oxygen can be absorbed directly through the skin, a process known as cutaneous respiration. This method is more effective in smaller turtles due to their higher surface area-to-volume ratio and when water is cold and oxygen-rich. However, cutaneous respiration is a minor contributor to overall oxygen uptake compared to lung breathing or even cloacal respiration.
Submergence Duration Factors
The length of time a turtle can remain submerged varies greatly, influenced by several environmental and physiological factors. These factors directly impact their metabolic rate and, consequently, their oxygen demand.
A primary factor is water temperature; colder water significantly reduces a turtle’s metabolic rate, decreasing its oxygen consumption and allowing for much longer dives. For instance, some turtles can hold their breath for up to four months during brumation in cold water due to their significantly lowered metabolism.
A turtle’s activity level also influences submergence time. A resting or sleeping turtle uses considerably less oxygen than an active one, enabling it to remain underwater for extended periods. While routine dives might last minutes, a resting turtle can stay submerged for several hours. Conversely, a stressed or highly active turtle will deplete its oxygen stores much more quickly and may need to surface frequently.
The availability of dissolved oxygen in the water can also affect how long a turtle can stay submerged, especially for those species relying on cloacal or buccopharyngeal respiration. Turtles can tolerate periods of anaerobic respiration, producing energy without oxygen, but this is a short-term solution that leads to the accumulation of lactic acid and is unsustainable for prolonged periods. This mechanism serves as a last resort when oxygen is scarce.