All living things need to draw breath, it’s just how they do it and the medium through which they get it that differs. Humans and other land-based animals have lungs that process dry air to obtain oxygen, which comes from plants that breathe it out after absorbing carbon dioxide.
Fish and other aquatic creatures, on the other hand, live in water, so they use gills to filter oxygen molecules present in the water. The octopus breathes air as other fish do, and since they have more than one heart, they need more oxygen than other mollusks.
Continue reading this article, and I will explain how an octopus can breathe air out of water. You’ll also learn about intertidal zones and how certain traditionally underwater species like octopi can comfortably step out of water.
What Sets the Indomitable Octopus on a Class of its Own?
Octopus is a name derived from the Greek, meaning eight footed. Among cephalopods, invertebrate mollusks such as cuttlefish and squid, octopi, and their nearest cousins, Argonauts are the only ones identifiable by eight arms.
The octopus is native to all the seas and tides of the world and can grow to span 13 feet in width, as is the Pacific Giant Octopus. This naturally occurring octopus on the American Northwest coast can have tentacle or arm lengths of 6.5 feet, resulting in width spans of 22 feet.
Except for octopi, cephalopods, from the ancient Nautilus to squid and cuttlefish, have what can be termed as the remnants of a shell. Squids have a gladius, a sword-shaped horny structure, while cuttlefish are so-called because of their cuttlebone, another evolutionary remainder of a shell.
The octopus has a complete absence of any shell material either externally or internally. All that an octopus has in the form of bone is a beak located in its mantel cavity, somewhere at the back of its bulbous head.
Inside this cavity are the gills, which also assist in pumping water in and out for the capillaries to pick up oxygen.
Octopuses also have three hearts, two of which pump blood through the capillaries in the gills to collect oxygen. This emphasizes how much oxygen the octopus requires and its immense reliance on the gills.
The third heart is dedicated to pumping the blood flow throughout the rest of its body. When the octopus is swimming, the third heart stops, and that’s why the animal prefers to crawl over rocks or coral as opposed to swimming.
How Does the Octopus Breathe?
The octopus is fully dependent on water to get their air exchange for oxygen and CO₂. For many underwater animals, coming out of water leaves their gills lacking buoyancy leading to collapse.
In this respect, the octopus has an advantage over other fish in that it can absorb oxygen through its skin from the water around it. The process by which this is accomplished is called passive diffusion.
If an octopus is not on the move, it can get about 40 % of its total O₂ requirements using its skin as a conduit. This figure drops by 10 percent when the octopus is engaged in swimming or other activities.
Immediately after an octopus eats is when it experiences the lowest level of passive fusion. During food digestion, oxygen absorption through its skill can drop to as low as 3%. As though that wasn’t enough, the octopus skin is covered with hemocyanin, a respiratory pigmentation that helps increase in-vitro oxygen uptake.
This is the ability that gives an octopus breathing ability when it’s on land, as the gills become ineffective since there’s no water. An octopus relies on the residual skin moisture, essentially drawing oxygen from the water remaining on its body.
As you can see, this is not an efficient breathing source, seeing as it can only deliver less than half of the octopus’s oxygen requirements. Even at peak efficiency, such trips over land are usually brief, normally from one tidal pool to another, or across a pebbled beach.
How Long Can Octopus Survive out of Water?
Octopi have to get the amount of oxygen required to satisfy the blood pump demands by those two hearts. Pumping of the mantle cavity pushes water forcefully over capillaries, enabling the octopus to absorb a saturation level of 11% in its blood.
In retrospect, other fish can only attain 3% O₂ saturation while relying on the standard water current flow through their gills.
The octopus is nocturnal, meaning if it’s to come out, it does so at night. Some octopus species with coastline habitats slip out of the ocean into tidal pools hunting crustaceans like crabs.
The land time kept by out of water octopus is minimal, as they rely solely on passive diffusion oxygen. Short excursions from one tidal pool to another probably lasts less than a minute, but if need be, they can survive out of water for a couple of minutes.
The Well-developed Gills of an Octopus
When the octopus is in the water, its main respiratory surface is its gills. These are composed of a series of branchial ganglia plus sets of once, twice, and thrice folded lamellae.
Primary demi-branches of these lamellae form secondary free folds that extend to form fan-shaped tertiary ones. Water moves over these intricate gill structures sucked in through the mantle cavity and out via the funnel.
In water at 20° C, an octopus attains up to 65% oxygen uptake with its gill’s high amount of oxygen absorption. Another estimated 40% of oxygen saturation can be achieved with in-vitro or through the skin, especially when the octopus is resting.
How Do the Three Hearts of an Octopus Function?
An octopus has three hearts, consisting of one main two-chambered heart that sends oxygenated blood to its body’s organs. The other two are smaller branchial hearts that are allocated to each set of respiratory gills.
The two gill-hearts send oxygenated blood to the systemic heart’s atrium, and the ventricle then pumps it to the rest of the octopus’s body.
Blood flows through three aortas from the main heart, and for each of the minor hearts, there’s an abdominal and gonadal aorta. A dorsal aorta is the main conduit for blood circulation throughout the octopus’s body.
Besides that, an octopus has blood sinuses, large pouches behind its eyes and around its gut that act as reserves for blood needed during physiological stress scenarios.
When the octopus employs jet propulsion to get along, the main heart goes through cardiac arrests. This can also be induced by any sudden stimulus, mantle pressure, or when its body is handling a high oxygen debt.
Any rapid movement will make an octopus suffer oxygen exhaustion, remembering that it’s moving eight sometimes very long tentacles. The octopus experiences an increase in stroke by up to three times the beating of the systemic heart in exertion.
Thanks to the well-developed receptors on the gills of an octopus, it’s able to control the amount of O₂ it pulls out of the water.
Also read: Do Fish Eat Seaweed?
Frequently Asked Questions
Can octopus walk on land?
Yes, although this is more of a waddle than a walk. Octopus can get out of the water and survive for a few minutes moving on land but must soon return into the water; otherwise, they’ll suffocate.
Can an octopus feel pain?
An octopus’s nervous system is well developed, and these invertebrate mollusks have a larger brain than most aquatic species. Octopuses have pain receptors, demonstrated by their withdrawing tentacles from noxious, pain-causing stimuli.
Why is octopus blood blue?
A protein called hemocyanin carries oxygen in an octopus’s blood instead of red blood cells or hemoglobin in mammals. This protein is dissolved in the octopus blood plasma and causes the blood to appear blue.
What is octopus ink?
Octopuses have a defensive strategy where they produce blank ink when confronted by predators. This ink is formed in a bladder-like sac and is released into the water to form a cloud by which the octopus can escape.
What does an octopus eat?
By catching food with its tentacles, an octopus then guides it to its beak-like mouth, which crushes the shells of the creature it preys on. These include crabs, mussels, sea snails, and other mollusks.
The octopus liquefies its prey while still in their shells using an enzyme and then sucks up the resultant protein goo.
Octopus out of water is a sight to marvel at, but most of that happens at night, so you’ll have to stay up very late by the beach to catch them at it. As long as its body stays moist, the octopus will capitalize on passive diffusion to absorb trace oxygen molecules that enable it to stay out of water for minutes.
One such case happened at the New Zealand national aquarium in 2016, when inky the octopus broke from her confinement and escaped through a drain pipe. This trickster crept out of her tank, crossed the aquarium floor, and crept through a 5.9-inch drain pipe.