Question on GPOs & how they eat crab... (NHZ)

[Sounder]

My parents are moving out near Port Angeles and I'm rather excited to have a staging area for Peninsula and Strait dives. In visiting them and looking at their new house, we spent some time in the town walking around and seeing what there was to see... and it wasn't much. They DID, however, have a pretty cool Marine Life Science Center or something (I forget what it's called).

They've got anemones, crabs, sea cukes, gunnels, tube worms, and some sculpins, etc. They've also got a cool lion nudi tank where the lion nudies are able to catch little micro-shrimp. Watching this was a first for me and was pretty cool. The highlight of the exhibit, however, is a small GPO (and yes, I looked and confirmed it was a GPO and not a Red when they said it was one).

They were feeding it a rock crab and discussing how it eats it saying that it first envelops the crab in a "balloon" of sorts using the webbing between it's arms to make a fairly closed water-chamber with the crab in it... then injects an anesthetizing bio-toxin into the water to render the crab "asleep." Following this the GPO bites into the crab to inject a protein-dissolving toxin that allows it to "suck out the insides like through a straw."

This is not exactly what I understood about how they eat a crab, but I'm hesitant to post what my concept of the process was as they were somewhat of an "official" giving this information versus me who's just a diver who likes octopuses.

Can someone please share what the process really is? Thanks!!

[dphershman]

Actually, that sounds pretty close to being right. The octo makes a quick bite and injects some saliva containing venom, killing the crab. See the book published last year called Octopus: The Ocean's Intelligent Invertebrate by Mather, Anderson and Wood. There's a chapter on digestion that describes this in detail (see page 62). Crabs have claws and I for one can say that they do pinch hard, a red rock crab uses its pinchers to break a moonsnail out of its shell, so a soft Octo has to be somewhat careful.

you can order it through Powell's books in Portland.

http://www.powells.com/s?kw=Octopus+The ... ent&class=

[Sounder]

Actually, that sounds pretty close to being right. The octo makes a quick bite and injects some saliva containing venom, killing the crab. See the book published last year called Octopus: The Ocean's Intelligent Invertebrate by Mather, Anderson and Wood. There's a chapter on digestion that describes this in detail (see page 62). Crabs have claws and I for one can say that they do pinch hard, a red rock crab uses its pinchers to break a moonsnail out of its shell, so a soft Octo has to be somewhat careful.

you can order it through Powell's books in Portland.

http://www.powells.com/s?kw=Octopus+The ... ent&class=

I will order the book, thanks!

In the meantime, to confirm... the octopus makes a quick bite to the under-side of the crab (carapace is almost always intact) with the paralyzing/killing venom, right? NOT an instant injection of venom into the chamber it's holding the crab in so the crab breathes the water/toxin in and goes to sleep.

This is more along the lines of what I understood, though I'm definitely going to get the book.

Thanks!!

[Grateful Diver]

On a side note ... my friend Janet works at that Marine Science Center. There used to be a display of some of my nudibranch pictures up there ... for the kids.



... Bob (Grateful Diver)

[nwscubamom]

Awesome about them moving to PA!! Yes, that's the Fiero Marine Life Center - and I've taught classes there even! (years ago). I think that's the first time I ran into the Washburn family, if I remember right. They had been diving that day and showed up to class in their wetsuits.

I am sure Greg can give us the scoop on this one, although it sounds a lot like how a moonsnail eats clams - using an enzyme to break down the muscles holding a clamshell shut or something like that.

- Janna

[Greg Jensen]

I wish I could give a definitive answer on this, but it's something I've wondered about too. In the old literature it always had them using their 'terrible beak' to rip into the crab's carapace, but as already noted here the carapace is undamaged when they finish eating.
Crabs do seem to be paralyzed awfully quickly, and it seems (given their thick shell and the octos hard beak) that you'd hear a crunch if they were immediately biting through the underside of their exoskeleton. In the video "Incredible Suckers" it supposedly shows a blue ring octopus knocking out a mantis shrimp from a distance by blowing toxin toward it. The idea that they're knocking out the crab by a waterborne toxin in the webbing is the most consistent explanation for the crab and octo behavior that I've observed, but I haven't seen any published accounts of it.
The 'sucking it out through a straw' sounds more like a spider than an octopus. I'm suspicious about this on two counts: if this were the case, why do they disarticulate the whole crab? And second, when I've overfed pet rubescens, they start to just eat the goodies in the main part of the body and leave the legs and claws behind. The meat in those still seems normal, not liquified.
Moonsnails use their radula and an acidic secretion to bore a nice round hole through the clam shell. I caught one in the act a couple years ago, with its proboscis extending through the hole and eating the clam. A moon snail researcher was surprised to hear this as she hadn't seen evidence of an extensible proboscis when dissecting them, and it was assumed that the bore hole was just used to get the clam open.

[Norris]

I was lucky enough to actually catch a GPO hunting, using the very methods you described, Sounder. I was a little curious as to what this Octo was doing, but after doing a little research it seemed it was hunting. Just go to the very end of this video to see what I am talking about.

[youtube]http://www.youtube.com/watch?v=cJIlDMK0oaA[/youtube]

[Sounder]

Yeah Rick, that is similar to what I watched... but the GPO I saw grabbed the crab and pulled it into the webbing "sack" versus what it appears the GPO in your video is doing by kind of projecting the webbing over the target. Very similar though, and perhaps same technique under different situations... a "thinking c'pod."

I also can't help but be excited that I asked a question Greg couldn't definitively answer!! Thank you for your answer - it was really interesting and I am definitely interested in learning more about it. We need a beak-proof "crab-cam!!"

[Cera]

I am glad to hear you reference the Octo book, I have been eyeing it. Do you like it? Is it worth the $$$? Looks beautiful.

[dphershman]

I am glad to hear you reference the Octo book, I have been eyeing it. Do you like it? Is it worth the $$$? Looks beautiful.

yep--- with lots of references to our local GPOs and Reds.

[gcbryan]

I asked Roland Anderson this question several years ago and I thought the answer was more or less that the radula secretes the enzyme and gets the meat out or the beak makes an opening, "spits" the enzyme in and then the radula takes over. I don't recall anything about an open water enzyme while the octo is cloaking it but I did wonder exactly how the octo gets the crab back to its den before eating considering the claws and the damage they can do.

I'm guessing they have several slightly different options as to how they work depending on circumstances. I've seen divers feeding crab to GPO (in their den) but you can't really see what is going on. The only time I witnessed something different going on a diver threw a crab in the den and all of a sudden it almost seemed as if one could see the results of whatever had happened. It was more like how you would expect the water to change if a crab shell was suddenly collapsed...almost like a sudden low pressure zone

If anyone has done any more research since this thread started please report back your findings.

As a side note, I did witness (Sund Rock) a Wolf Eel coming back from hunting for dinner with a Dungeness Crab in its mouth. It carried it back to its den and then just crunched down, shell and all, almost like a snake eating a mouse. I assume the shell had to be discarded later but it wasn't discarded while we were watching.

[Tidepool Geek]

Greetings,
Sorry to come to this thread (and this forum) so late; I only learned of it recently.

By way of introduction, my name is Alex Hirsekorn and I’ve been a volunteer docent at the Feiro Marine Life Center in Port Angeles, WA for approx. 10 years. I am not a diver.

The original question in this thread concerns how a GPO captures, subdues, and consumes a crab and whether or not that process is described correctly at the Feiro Center.

To begin, here is the basic spiel that we present to our visitors (anywhere from 5 to 20 times per day):

1. When the octopus decides to take a crab it envelops said crab in a bag formed by the webbing between the octopus’ arms. It should be noted that the way the octopus goes about this envelopment is entirely situational and different techniques will be used under different circumstances.

2. The octopus (hereinafter GPO) has two sets of salivary glands and conscious control over which set it uses. Once the crab is sealed up the GPO ‘spits’ saliva A (more properly “cephalotoxin”) into the bag – Saliva A is basically a sedative and puts the crab to sleep without killing it. If the crab is taken away from the GPO at this point it will recover its senses very quickly and run off.

3. Now that the crab is knocked out the GPO will bite through the shell (or pull off a leg or two) and inject saliva B into the crab. Since the crab is still alive at this point he pumps saliva B (which is a really powerful digestive enzyme) throughout its body and, in effect, digests itself on the GPO’s behalf.

4. The GPO generally naps a bit while this process is going on but when the crab is done* it is dismembered such that the GPO can suck out what amounts to crabmeat Jell-O

*We used to say this process takes 1.5 to 2 hours based on observations at our facility; based on new outside information and new observations in house we now believe this ‘pre-digestive’ process is far faster; on the order of 15 or 20 minutes.

Sometime after learning of the questions posted on this forum I had the opportunity to discuss the topic with Victoria BC based GPO researcher James A. Cosgrove. For anyone not familiar with him, Jim Cosgrove has been formally studying wild GPOs for 30 years or more and probably knows as much about the habits of this species as anyone in the world. I gave Jim our spiel as shown above and asked him for any corrections of fact or tenor; he had two corrections for us which are shown above in blue.

The bottom line is that the description above is accurate to the extent we can make it so. It is also quite basic; please keep in mind that 90% of our visitors have virtually no prior knowledge of the marine environment and our mission is to teach whatever a given visitor is willing and able to handle. That equates to keeping our discussion of this and other topics at a very elementary level until such time as a visitor asks for more.

As an aside, the Feiro Center generally tries to keep a GPO on display at all times. We do our collecting in May for the most part and then keep the animal for 6 to 18 months depending on how old it is when we bring it in. In past years we have avoided Octopus rubescens because of its proclivities for biting and escaping. We’re hoping to change that in the future but we’re still working to address the issues of tank security and handler safety.

Finally, a couple of nit-picks:

1. Our facility’s name is spelled Feiro and pronounced like Faro (the card game) or Pharaoh (Egyptian ruler). Fiero was a Pontiac sports car.

2. The plural of Octopus is not Octopi! In North America the plural is, by convention, Octopuses; in Europe, I believe, they use the more historically accurate word Octopodes.

It has been said that there are two types of information in the world
a. Interesting
b. Useful

I hope this is found to be one or the other.

Octopodally yours,
Alex

[ktb]

Thanks Alex! Your post was both interesting *and* useful!! Welcome to NWDC.

[spatman]

Fantastic post, Alex. Thank you and welcome.

[Jan K]

Fantastic post, Alex. Thank you and welcome.

[John Rawlings]

Welcome to NWDC, Alex!

[LCF]

Thank you very much for taking the time to share that information with us! Our experience of the underwater world when diving is infinitely richer for knowing more about the animals we watch.

[enchantmentdivi]

2. The plural of Octopus is not Octopi! In North America the plural is, by convention, Octopuses; in Europe, I believe, they use the more historically accurate word Octopodes.

Hallelujah! Hallelujah! Hall-eee-eh-lujah!

I like you already.

[airsix]

Finally! Someone who won't look at me funny when I say octopodes (ock-top-O-dees)! I say it because it's fun. Welcome! By the way, octopodally is my new favorite word. The original poster just got a txt from me to come read the great new info. Thanks and welcome!

[Sounder]

Yes, thanks for the thorough description Alex. That helps a lot. My family enjoys coming down to the (not-a-car) marine center when we visit my parents in Port Angeles. It was very fun to watch the octopus in the tank envelope the crab in the "balloon of salaiva A" while we were there.

Thanks again for posting this information, and welcome to our group!

-Doug

[diverden]

FYI every dictionary I can get my hands on lists 'octopi' as a valid form of the plural along with 'octopuses'. Sadly, my circa 1970 condensed OED is in a box somewhere in the basement. See why octopi is considered "correct" albeit linguistically inaccurate: http://www.youtube.com/watch?v=wFyY2mK8pxk
http://www.grammarist.com/usage/octopi-octopuses/