Octopus arms are smart arms

February 14, 2014 

n octopus settles in on the Spiegel Grove, a bit annoyed at our intrusion.


Last weekend my dive buddy Phil observed, up close and personal, a single dangling tentacle of a Man of War. We were descending on a mooring line and all of the sudden, I saw him shaking his hand back and forth quite rapidly. 

We had seen a few Man of Wars on the surface, but this tentacle was just below the ball, wrapped around the line. Please be careful going down the lines. I hope these floating pain dispensers are not here for long. As you may recall, a few years ago they were prolific throughout the Upper Keys.

That got me to thinking about tentacles. I will be learning more about the pain inflicting types in the next few weeks, but for now I'll begin with the variety I see the most, and have a great fascination with -- octopus arms.

On my overseas trips, I have had a great time photographing different types of these critters, some larger, most smaller than our common octopus in the Caribbean. While I was poking around, I found a fair number of references on how the octopus population may affect the stone crab claw fishery. I will save that discussion for another day.

I love watching the fluid motion of an octopus. I look at it this way: commanding two arms and two legs is sometimes an ordeal for some divers -- imagine having twice the appendages to steer around on a daily basis! That colossal coordination alone gets my respect.

My curiosity is centered on the arms, as I said. I found some great information on American Scientific from the octopus lady, Katherine Harmon Courage. She has a book on octopuses available on Amazon, and I read the few pages that are available in the sneak peak. I think this will be a good read when I make the time for it. She has lots of great entries in her blog, the Octopus Chronicles. See http://blogs.scientificamerican.com/octopus-chronicles/ 

There is more information here than I can wrap my arms around. And with an octopus, that could be more relevant than you might think at first. Octo-arms are smart arms. Over two-thirds of an octopus' neurons are in the arms, not in the main part of the brain.

Even more bizarre, the arms continue reacting after they are severed from the body. Reminds me of the "Thing" that ran around the Addams Family mansion. Researchers postulate this is a function of the way the octopus searches for food. With each arm capable of reacting independently, the arms are more likely to stay intact when encountering unseen things in the crevices and cracks they investigate for a meal.  See http://blogs.scientificamerican.com/octopus-chronicles/2013/08/27/even-severed-octopus-arms-have-smart-moves/ for this narrative.

Once the octopus finds it prey, the suction cups spring into action in the capture. In another interesting blog entry, Ms. Courage describes the characteristics of the suction cups. They can actually taste the water. I guess that explains why a recent encounter I had with an octopus made him spit my finger out as soon as he touched it. I'm just not an octopus' cup of tea.

It was a funny encounter. I found a few freshly cleaned shells in a neat little pile, so I peaked in the adjacent hole, and an eye and an arm greeted me. We made eye contact, so I put my finger at the edge of the lair. He reached out, gave me a little grip on the finger, then pulled his arm away, but did not retreat. 

We sat there gazing at each other for a few seconds. I wanted him to come out an play, but I guess he was quite comfortable with a full belly, kicked back on his couch. So I left him as he was, hoping to see him the next time I visit his yard. I marked the spot on my reef memory chart.

In Europe, they have an entire research consortium dedicated to the octopus -- the goal is to emulate the functions and mechanics of the animal into a new generation of flexible, soft-bodied robots. An android with a twist -- or that can twist, literally. You can see the background paper here: http://timgimages.com/PDF/EU_Octopus.pdf 

In another study, scientists measured the elongation of octopus arms in a test tank. They can stretch their arms more than two times the resting arm length. Smaller octopuses can stretch further, and an unexpected finding was females can outstretch males of similar size, reaching nearly three times normal arm length. Sort of reminded me of a former girlfriend... it seemed I was never out of her reach, even on guys night out. Check out the stretchy video here: http://www.bbc.co.uk/nature/21966304 

One more thing: on Feb. 8, I attended an event for The Everglades Foundation for the release of their new book, Florida Bay Forever, commemorating the twentieth anniversary of the foundation. This took place at the Florida Keys History and Discovery Center at the Islander Resort.  

Go and see the Clyde Butcher images on exhibit there now. If you have not seen this book, you should. I was honored to be included as a contributor. It is visually stunning and expertly written. Please extend one of your arms and grab a copy of Florida Bay Forever here: http://www.evergladesfoundation.org 

Tim Grollimund is a freelance photographer and PADI divemaster based in Key Largo.  He can be reached at tim@timgimages.com.  Tim is a member of the Florida Keys National Marine Sanctuary Advisory Council.  Opinions expressed by Tim are not the official views of the FKNMS.

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