"Argonaut" Octopus Sucks Air Into Shell As Ballast

audiovideodisco writes "Even among octopuses, the Argonaut must be one of the coolest. It gets its nickname — 'paper nautilus' — from the fragile shell the female assembles around herself after mating with the tiny male (whose tentacle/penis breaks off and remains in the female). For millennia, people have wondered what the shell was for; Aristotle thought the octopus used it as a boat and its tentacles as oars and sails. Now scientists who managed to study Argonauts in the wild confirm a different hypothesis: that the octopus sucks air into its shell and uses it for ballast as it weaves its way through the ocean like a tiny submarine. The researchers' beautiful video and photographs show just how the Argonaut pulls off this trick. The regular (non-paper) nautilus also uses its shell for ballast, but the distant relationship between it and all octopuses suggests this is a case of convergent evolution."

Comments

Convergent Evolution?

[Shadow Wrought]

Nah. The Angels just mis-intrepeted the cocktail napkin with God's first specs on it. Then they had to go back and create the same design with hardware instead of software.

That's not ballast.

[jcr]

Ballast is weight that counteracts buoyancy. By introducing air into its shell, the animal is adding buoyancy.

-jcr

Re:That's not ballast.

[jcr]

If it had the ability to liquify air, that would be far more interesting.

-jcr

Re:That's not ballast.

[Rene S. Hollan]

Nope.

The argonaut traps air, and then forcefully descends to depth. So long as it has not reached the appropriate depth, it has to keep thrusting itself downward with it's jet, but once there, it is neutrally buoyant and no further expenditure of energy is required.

It if can't get deep enough, then ultimately it will tire and the buoyancy will bring it to the surface again.

Re:That's not ballast.

[Daniel_Staal]

As the pressure increases with depth, the volume of the air will decrease as it is squeezed into a smaller space. Buoyancy is determined by density, which is mass per unit volume. Mass is staying the same, but volume is decreasing.

Above a certain depth, they will be be positively buoyant, and rise. Below that depth, they will be negatively buoyant, and sink. They gather enough air to be neutral at a certain depth, and stay there. The more air they gather the lower that depth is. If they can't get deep enough, they will tend to rise back to the surface (unless they vent air).

The article is right.

Re:That's not ballast.

[CoryD]

And here I thought in submarine movies the term, "blow the ballast tubes" indicated releasing sea water that is held inside the tubes to allow for bouyancy. Hence, allowing for a sharp decrease in depth. So yes, while "ballast" does indicate a weight keeping a ship or object submerged, it can also be used as a "ballast tube" that causes lift.

Re:That's not ballast.

[pixelpusher220]

From the comments on TFA: As the Argonaut decends, the volume of air decreases under the increased water pressure. That causes the air to be less buoyant. So with more air, the air pocket maintains its buoyancy force for deeper dives. The Argonaut still has to 'force' its way down to the depth of neutral buoyancy though.

Also from the comments, the Nautilus traps more air and has a hard shell so they can resist the water pressures more than the Argonauts. This allows the Nautilus to dive to deeper depths than the Argonaut.

Re:That's not ballast.

[MasterPatricko]

Yes, a buoyancy control device (BCD) - usually an inflatable vest connected to your air cylinder - is standard diving equipment.

Scuba divers will know that to stay neutrally buoyant, as you dive deeper, you must add extra air to your buoyancy control vest, and vent air when rising.

Being neutrally buoyant is an unstable equilibrium, so if you are changing depth and do nothing or if you get your correction wrong, you end up rising/sinking even faster.

If you do maintain your buoyancy well, your energy usage (for example for divers, as measured by your air usage) is hugely reduced - it makes sense to get it right if you plan to spend significant time at a roughly constant depth.

The only difference in this case, is that the argonaut has no easy push-button to change buoyancy mid-dive, and instead has to return to the surface every time.

Re:That's not ballast.

[jcr]

When you "blow the tubes" you're using compressed air to force the water out. The water is the ballast.

-jcr

Neato (:

[DarkKnightRadick]

And for it's next trick, the octopus will change its color!

Oh wait, some already do that.

I for one

[Ka D'Argo]

hail our new submarine octopus overlords

Re:This isn't news.

[SQLGuru]

The news is that we now understand how and why they do it.

Ubuntu?

[Saeed al-Sahaf]

"Argonaut Octopus" ... That's the new Ubuntu release, right?

Re:Mating Rituals

[ivandavidoff]

There's ugly, there's coyote ugly, and there's argonaut ugly.

Re:I beg to differ on definition of "Coolest"

[Rene S. Hollan]

It grows back: "Males generally form a new hectocotylus in each new season."

Debated for millenia?

[pdxp]

From TFA (emphasis mine):

Finn and Norman filmed and photographed live animals in the act of trapping their air bubbles, solving a mystery that has been debated for millennia.

Somehow I am starting to think that exaggeration in the media goes too far sometimes....

Re:Debated for millenia?

[ivandavidoff]

FTFA: No less a thinker than Aristotle put forward a hypothesis.

That was about 2.35 millenniums ago.

Re:I beg to differ on definition of "Coolest"

[HeckRuler]

Argonaut, Part Duex, bad to the bone!

Re:Mating Rituals

[somersault]

The arm doubled as a penis, snapped off during sex and stays inside the female’s body.

Yep, this has happened to me quite a few times. I'm just glad these things grow back!