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By Rebecca Morelle
Science reporter, BBC News
An octopus and its coconut-carrying antics have surprised scientists.
Underwater footage reveals that the creatures scoop up halved coconut shells
before scampering away with them so they can later use them as shelters.
Writing in the journal Current Biology, the team says it is the first example
of tool use in octopuses.
One of the researchers, Dr Julian Finn from Australia's Museum Victoria, told
BBC News: "I almost drowned laughing when I saw this the first time."
He added: "I could tell it was going to do something, but I didn't expect this
- I didn't expect it would pick up the shell and run away with it."
Quick getaway
The veined octopuses ( Amphioctopus marginatus ) were filmed between 1999 and
2008 off the coasts of Northern Sulawesi and Bali in Indonesia. The bizarre
behaviour was spotted on four occasions.
The eight-armed beasts used halved coconuts that had been discarded by humans
and had eventually settled in the ocean.
Dr Mark Norman, head of science at Museum Victoria, Melbourne, and one of the
authors of the paper, said: "It is amazing watching them excavate one of these
shells. They probe their arms down to loosen the mud, then they rotate them
out."
After turning the shells so the open side faces upwards, the octopuses blow
jets of mud out of the bowl before extending their arms around the shell - or
if they have two halves, stacking them first, one inside the other - before
stiffening their legs and tip-toeing away.
Dr Norman said: "I think it is amazing that those arms of pure muscle get
turned into rigid rods so that they can run along a bit like a high-speed
spider.
"It comes down to amazing dexterity and co-ordination of eight arms and several
hundred suckers."
Home, sweet home
The octopuses were filmed moving up to 20m with the shells.
And their awkward gait, which the scientists describe as "stilt-walking", is
surprisingly speedy, possibly because the creatures are left vulnerable to
attack from predators while they scuttle away with their prized coconuts.
The octopuses eventually use the shells as a protective shelter. If they just
have one half, they simply turn it over and hide underneath. But if they are
lucky enough to have retrieved two halves, they assemble them back into the
original closed coconut form and sneak inside.
The shells provide important protection for the octopuses in a patch of seabed
where there are few places to hide.
Dr Norman explained: "This is an incredibly dangerous habitat for these animals
- soft sediment and mud couldn't be worse.
"If they are buried loose in mud without a shell, any predator coming along can
just scoop them up. And they are pure rump steak, a terrific meat supply for
any predator."
The researchers think that the creatures would initially have used large
bivalve shells as their haven, but later swapped to coconuts after our
insatiable appetite for them meant their discarded shells became a regular
feature on the sea bed.
Surprisingly smart
Tool use was once thought to be an exclusively human skill, but this behaviour
has now been observed in a growing list of primates, mammals and birds.
The researchers say their study suggests that these coconut-grabbing octopuses
should now be added to these ranks.
Professor Tom Tregenza, an evolutionary ecologist from the University of
Exeter, UK, and another author of the paper, said: "A tool is something an
animal carries around and then uses on a particular occasion for a particular
purpose.
"While the octopus carries the coconut around there is no use to it - no more
use than an umbrella is to you when you have it folded up and you are carrying
it about. The umbrella only becomes useful when you lift it above your head and
open it up.
"And just in the same way, the coconut becomes useful to this octopus when it
stops and turns it the other way up and climbs inside it."
He added that octopuses already have a reputation for being an intelligent
invertebrate.
He explained: "They've been shown to be able to solve simple puzzles, there is
the mimic octopus, which has a range of different species that it can mimic,
and now there is this tool use.
"They do things which, normally, you'd only expect vertebrates to do."