Manatees, often called sea cows, are large, gentle marine animals that spend their entire lives in the water. Despite their aquatic existence, they do not breathe like fish. The simple answer to whether manatees breathe underwater is no. As mammals, manatees rely completely on atmospheric air and must regularly surface to take a breath. Understanding how they manage this necessity reveals unique biological features that allow them to thrive in shallow-water habitats.
The Requirement for Air
Manatees are classified within the order Sirenia, making them aquatic mammals, just like whales and dolphins. As mammals, they possess lungs for respiration rather than gills. This means they must obtain oxygen directly from the air above the water’s surface. Drowning is a danger if a manatee is prevented from reaching the surface for an extended period.
Their dependence on air requires them to constantly manage time between dives and trips to the surface. They cannot extract dissolved oxygen from the water. Their respiratory system is designed to maximize the efficiency of each breath taken in the atmosphere. This reliance on air drives their behavior, physiology, and distribution in shallow, calm waters.
Physiological Adaptations for Extended Submergence
Manatees possess specialized physiology that allows for impressive breath-holding capabilities. When resting, they can remain submerged for up to 20 minutes, far exceeding the duration of most land mammals. This extended breath-hold is possible due to an extremely low metabolic rate, which significantly reduces oxygen consumption.
When diving, manatees exhibit the mammalian diving reflex, where the heart rate slows considerably (bradycardia). This reflex conserves oxygen by prioritizing blood flow to the brain and vital organs. Their large, flattened lungs are horizontally oriented along their backs. This structure aids in buoyancy control, allowing them to adjust depth by changing the air volume in their lungs.
The muscular diaphragm is distinct, featuring separate “hemi-diaphragms” instead of a single muscle. This dual design contributes to efficient breath exchange. In a single respiration, a manatee can exchange approximately 90% of the air in its lungs, compared to a human who typically exchanges only about 10%. This high rate rapidly replenishes oxygen stores, preparing them for submergence.
The Mechanics of Respiration
The act of breathing for a manatee is a precise and highly efficient process that occurs at the water’s surface. When resting, a manatee typically surfaces to breathe every three to five minutes, though they can remain underwater for much longer. When active, the frequency increases significantly, sometimes requiring a breath every few minutes.
To take a breath, the manatee only needs to break the water’s surface with its snout and nostrils. They do not need to expose their entire head, which helps maintain their streamlined body position. Their nostrils are equipped with muscular valves that automatically close tightly when the animal is underwater.
These “valvular nostrils” prevent water from entering the respiratory system during submergence, opening only when the manatee surfaces. The entire process of exhalation and forceful inhalation is often completed in less than two seconds. This rapid gas exchange, facilitated by their powerful diaphragm and high lung capacity, allows the manatee to minimize its time at the surface and quickly return below.