Octopuses cannot breathe air like land animals. Their respiratory system is specifically designed for extracting oxygen from water. While they can venture onto land, this ability is temporary and limited by their aquatic adaptations. Sustained terrestrial survival is not possible for an octopus.
Aquatic Respiration
Octopuses primarily breathe underwater through specialized organs called gills, located within their mantle cavity. Water is drawn into the mantle cavity. As the water passes over the gills, tiny blood vessels called capillaries absorb dissolved oxygen.
The gills are feathery, featuring numerous thin filaments that significantly increase the surface area for gas exchange. Each of the octopus’s two gills has a dedicated “branchial heart,” which pumps blood through the gills to pick up oxygen. The oxygen-rich blood then returns to a third, systemic heart, which circulates it throughout the rest of the body.
This highly efficient circulatory system allows octopuses to effectively extract oxygen from their aquatic environment. Once oxygen has been absorbed, the deoxygenated water is expelled from the mantle cavity through a muscular tube called the siphon. This method of respiration is optimized for water, making the transition to air problematic.
Brief Excursions
Despite their aquatic nature, some octopus species are occasionally observed leaving the water for short periods. This behavior is motivated by hunting for prey like shellfish or snails in tide pools, escaping predators, or moving between isolated bodies of water. These excursions are brief, often lasting only a few minutes, though some octopuses can survive out of water for up to 20-60 minutes under ideal conditions.
During these temporary terrestrial movements, octopuses can absorb a limited amount of oxygen directly through their moist skin, a process known as cutaneous respiration. This skin breathing can contribute a notable percentage of their oxygen intake, but is far less efficient than gill respiration and insufficient for sustained survival. High humidity is important for maintaining skin moisture, which facilitates this limited gas exchange and prevents rapid drying.
Risks of Terrestrial Exposure
Prolonged exposure to air presents risks to an octopus due to its specialized aquatic respiratory system. When an octopus is out of water, its delicate gills, which are designed for buoyancy and efficient gas exchange in a liquid medium, can collapse. This collapse drastically reduces the surface area available for oxygen absorption, impairing their ability to “breathe” in air.
Another threat is desiccation, or drying out. Octopuses have soft bodies and permeable skin, making them susceptible to water loss in an aerial environment. The warmer and drier the air, the faster they dehydrate, leading to physiological problems. Without the support of water, their own body weight can also become a burden, making movement difficult and potentially damaging internal organs. Ultimately, the combination of gill collapse and desiccation leads to a lack of oxygen, resulting in suffocation and death if they remain out of water for too long.