November 24, 2011 | 2
The slimy-looking cephalopod, captured in a rare video crawling over land, has many people (queasily) asking whether such bizarre-looking behavior is unusual for these animals.
The video, recorded at the Fitzgerald Marine Reserve in San Mateo County, California (originally uploaded in June but promoted earlier this week on Boing Boing), shows an octopus laboriously lugging itself over a tidal area before disappearing back into the water.
I checked in with Julian Finn, a senior curator of marine invertebrates at the Museum Victoria in Australia, and James Wood, a marine biologist and curator of The Cephalopod Page, to see what they thought about this slinking cephalopod.
“Crawling along out of water is not uncommon for species of octopus that live in the intertidal or near shore,” Finn says. Wood has seen several different species of octopuses getting around this way in the course of his research. As he points out, however, most species of octopuses are nocturnal, so we humans are less likely to catch them creeping out of the ocean.
Why would an octopus struggle across land, when its boneless body seems so unfit for moving out of water? For the chance to find some tasty shellfish and snails, most likely. When the tide goes down, “many octopus species emerge to hunt in the pools of water left behind by the receding tide,” Finn notes.
The crab shell that the octopus drops midway through the video might be evidence of this dinner motive. “Octopuses often carry prey items when foraging, returning to their lairs to consume them,” Finn says. “It is possible that the octopus in the video was either finished consuming the contents of the crab or was too tired to continue carrying it on land.”
After an octopus has cleared one tidal pool of food, it will often then haul itself back onto land in search of the next pool, which, Wood notes, it might be able to spot visually, or detect ahead with its outstretched arms.
Lurching onto land can also be an escape tactic if a pool-hopping octopus senses danger, such as, Finn notes, “a larger octopus.” Or a human, Wood says.
“Once while I was in Bermuda I was chasing and photographing a common octopus when it crawled out of the water, across eight feet of rocks and went back into the water,” Wood recalls. “If I was a fish instead of an air breathing mammal, I would not have been able to follow it.”
Octopuses themselves depend on water to breathe, so in addition to being a cumbersome mode of transportation, the land crawl is a gamble. “If their skin stays moist they can get some gas exchange through it,” Wood notes. So in the salty spray of a coastal area they might be okay to crawl in the air for at least several minutes. But if faced with an expanse of dry rocks in the hot sun, they might not make it very far.
Illustration courtesy of Ivan Phillipsen