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I saw videos of octopuses crawling on the ground and I was wondering how long an octopus can survive when out of the water? Does it depend on either its size (i.e., does a big octopus from deep sea survive longer than a tiny octopus) or the species?

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The Pacific Northwest Tree Octopus only needs water during the early parts of its lifecycle; the rest of the time, it can get what it needs from rain or atmospheric moisture. – Mark Feb 18 at 20:41
Umm.. the Tree Octopus bit is a hoax.. If you read a little of the linked page, above, it mentions its natural predators being the Bald Eagle ..and sasquatch. – elrobis Feb 18 at 22:15
Wow I actually bought that tree octopus story, quite a convincing hoax – Christiaan Feb 19 at 8:02
up vote 33 down vote accepted

Short answer
Under ideal conditions, an octopus may survive several minutes on land.

Octopuses have gills and hence are dependent on water for the exchange of oxygen and carbon dioxide. Gills collapse on land because of the lack of buoyancy (source: UC Santa Barbara). Octopuses have three hearts. Two of these are dedicated to move blood to the animal’s gills, emphasizing the animal's dependence on its gills for oxygen supply. The third heart keeps circulation flowing to the organs. This organ heart actually stops beating when the octopus swims, explaining the species’ tendency to crawl rather than swim (source: Smithsonian).

According to the Scientific American, crawling out of the water is not uncommon for species of octopus that live in intertidal waters or near the shore (Fig. 1). Because most species of octopus are nocturnal, we humans just don't see it often. Their boneless bodies are seemingly unfit for moving out of water, but it is thought to be food-motivated, e.g. shellfish and snails that can be found in tidal pools.

Octopuses depend on water to breathe, so in addition to being a cumbersome mode of transportation, the land crawl is also a gamble. When their skin stays moist, a limited amount of gas exchange can occur through passive diffusion. This allows the octopus to survive on land for short periods of time, because oxygen is absorbed through the skin, instead of the gills. In moist, coastal areas it is believed they can crawl on land for at least several minutes. Mostly they go from pool to pool, never staying out of the water for extended periods. If faced with a dry surface in the sun, they will not survive for long (source: Scientific American).

Fig. 1. Octopus on land. Source: BBC

Your sub questions; I think small octopuses may survive longer, since passive gas exchange is the mode of survival on land. In general, an increase in diameter causes the volume to increase with a third power, while surface increases with a power of two. Therefore, an increase in body size reduces the surface-to-volume ratio and leads to reduced gas exchange. Because passive gas exchange needs large surface-to-volume ratios, I am inclined to believe small octopuses may cope better with terrestrial environments. However, in hot, arid conditions it is likely a bigger one will have an advantage, because it can store more oxygen in its blood.

In terms of species, I have to say I couldn't find any sources going in so much detail on this. Likely, as said, smaller species may do better in cool, moist conditions, while larger specimens may be better off in dry environments.

- Harmon Courage, Sci Am; (November 2011)

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Thanks for your complete answer. – Manuella Feb 18 at 9:37
Volume increases to the 3/2 power of surface. This is not exponential. It's not even quadratic. (It is faster than linear.) – Rex Kerr Feb 18 at 14:15
That's better! But the 3/2 power relationship holds for any shape that is scaled to different sizes, not just spheres. (It does not hold if shape changes with size. Tiny octopuses (e.g. blue-ringed) are generally not exactly the same shape as giant ones (Enteroctopus sp.).) – Rex Kerr Feb 18 at 14:45
@RexKerr - again many thanks for clearing up on my math. I have generalized that point in my answer. – Christiaan Feb 18 at 14:46

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