A clever octopus made headlines earlier this year after it swiftly disassembled part of its tank at the Santa Monica Pier Aquarium in California. But out in the open ocean its relative, the veined octopus (Amphioctopus marginatus), has upped the cephalopod intelligence quotient by using coconut shells as tools.
The dexterous octopuses were observed stockpiling discarded coconut halves, carrying them (with some difficulty), and later using the oversize pieces to build a protective armored covering, reports a team of researchers in Australia and the U.K. in a paper published online today in Current Biology.
But might the undulating invertebrates just be making use of found objects like an ant transporting food on a leaf or a hermit crab crawling into an empty shell?
These are true tool users, the researchers assert, placing veined octopuses in the rare ranks of birds, chimpanzees, humans and a few other mammals that put objects to more complex use. The invertebrates indeed purposefully collect, transport and then assemble the coconut shells for deployment only when needed (see video below).
"There is a fundamental difference between picking up a nearby object and putting it over your head as protection versus collecting, arranging, transporting (awkwardly), and assembling portable armor as required," Mark Norman, of the Museum Victoria in Australia and paper co-author, said in a prepared statement. "The fact that the shell is carried for future use rather than as part of a specific task differentiates this behavior from other examples of object manipulation by octopuses, such as rocks being used to barricade lair entrances," the researchers wrote in their paper.
And even though they boast eight flexible legs and handy suction cups, the octopuses face challenges in carrying these coconut halves. To do so, they flip the shells—which are larger than the octopuses' bodies—so that the open side is up and grasp it underneath with the upper part of their legs, holding it above the ground and walking stiffly on the soft substrate—an "ungainly" process the researchers call "stilt walking."
Indeed, one of the distinguishing features of this behavior is that carrying the shells is not an immediate advantage—but rather a burden and even a danger, leaving the animal more exposed to predators. But the risk seems to be worth the reward.
"While I have observed and videoed octopuses hiding in shells many times, I never expected to find an octopus that stacks multiple coconut shells and jogs across the seafloor carrying them," Julian Finn, of the Museum Victoria in Australia and also a co-author, said in a prepared statement.
After spending some 500 diver-hours over the course of 10 years, researchers off the coast of Indonesia observed several veined octopuses engaging in this behavior, with four instances of the animals carrying the coconut shells as far as 20 meters.
"I could tell that the octopus, busy manipulating coconut shells, was up to something, but I never expected it would pick up the stacked shells and run away," Finn said. "It was an extremely comical sight—I have never laughed so hard underwater."
Building an octopus' garden in the shade: Octopuses collect coconut shells and use them to create protective armor