Dive Dry with Dr. Bill

#589: Eight Arms to Hold Yous

Once again I'm going to titillate my readers with another story about my favorite "M" word. Parents beware. I've done too much of the other "M" word, Munching, lately so I'm trying not to dwell on it and to eat healthy so I can fit into my new wetsuit courtesy of Indian Valley SCUBA! But one can never do enough of the other "M" word... at least as long as one wants one's species to persist and their own genes to be represented in future generations! Yes, I'm talking about Mating... again... and again... and again. Of course in my case I don't have to be successful at it, but I still enjoy practicing.

I was out on one of my occasional day dives the other week. This time of year I mostly do night dives so I can enjoy the best of both "M" words without all the crowds that enter our water during the day. No, I'm not a vampire diver. Despite my fangs, I generally don't bite... except on full moons. Even then it's just a gentle love bite... unless your blood type is A! Oops, back to the dive before I get carried away (possibly in a straight jacket).

I was returning to the stairs from the far end of the dive park, about halfway through the air in my tank, when I stopped to film something. I had had some luck filming the rare California blue dorid nudibranch (Felimare californiensis) and a fragile rainbow star (Astrometis sertulifera) at the far end, but I can't even remember what it was I stopped to film at this point. As I was setting up the shot, I looked down and happened to see an octopus (probably Octopus bimaculatus) just "sitting" on the bottom. I thought it was pretty strange that it hadn't moved since I was within a foot or so of it.

I started filming and observing this octopus from up close and personal. I actually had to back up a bit to get my lights on it. Its behavior was rather unusual. It seemed to be moving its body as if it were mating, but I could not see another octopus in the vicinity. To the best of my knowledge they don't do it "solo." It was also strange that it did not try to escape from me and my prying camera. Perhaps it was just egotistical and thought I'd make it a movie star... or maybe it expected a modeling fee.

Then it moved away about a foot and I saw it had been resting on top of a hole in the cobbles, which I thought made things even stranger. Being the highly trained marine biologist that I am, the thought crossed my mind that there might be a mate somewhere in this hole. I sat and observed while filming the other octo which remained very close by. After a few minutes, another octo appeared and crawled out of the hole. Yep, my first thoughts were correct... it was indeed mating (and not solo). It was just that the object of its affection (or is it an affliction?) was down under the rocks.

Now the male octo can copulate from a distance... well, no more than an arm's length away It uses a modified third arm called the hectocotylus to transfer sperm capsules (spermatophores) to the female's mantle cavity. The end of this arm is flattened and spoon shaped. We biologists call it a ligula. Males may use it to scrape spermatophores from previous matings from the female and then insert their own to ensure their own paternity.

One truly amazing thing about the octopus' ligula is that it is not very conspicuous in every day life. That is a good thing since it lacks the pigment cells found in the rest of the body that allow octopus to change color and camouflage as protection from predators. Therefore the ligula is white in color. Now no octopus in its right mind would want to have such a highly visible arm as it goes about its normal routine. It just wouldn't be prudent! The ligula is tiny and obscure while the octo is indulging in the other "M" word, munching.

But when it is "in the mood" for that other "M" word, no male octo (or human) is in their "right mind." Amazingly, the octo's ligula is just like the human penis or clitoris in that it is erectile. Blood may be diverted into it and cause it to expand in size substantially. This permits the male to transfer much larger sperm packets, thus increasing the probability of conception which is what all species are about... ensuring their continuity. Fortunately the large, white ligula is inserted into the female's body cavity so it is not visible to predators. However, we all know that in the throes of passion rational thinking often goes right out the door. Coupling does increase the chance of a predator locating you... at least if you're an invertebrate. None did in this case.

Now octo sex is pretty rough and tumble. Heck, when you have eight arms that often do their own thing, it is quite different from a loving hug! Arms (often called tentacles by the misinformed landlubber) fly through the air (er, water) from both individuals. When I first observed and filmed this years ago, I wasn't quite sure if it was aggressive behavior or "love" making. I asked Dr. Eric Hochberg, who grew up on the island and became a noted cephalopod expert, what I gad filmed and he concurred it was lust. Well, OK, he actually used a more scientific technical term for it. Of course for many species, reproduction often requires getting over a fear of contact so they are occasionally interlinked.

There's another similarity between octopus love making and that of humans. Years ago I first observed and filmed it while on a dive at Ship Rock. I saw a lustful male chasing after a lady octo and started the camera rolling, thinking I knew exactly what to expect. As he closed in for "the kill," the object of his affection let loose... with two squirts of her dark ink. Now usually octos use their ink as a defense against predators. However, this female used it to warn off the potential mate. Perhaps he was a sexual "predator?" Of course most males who frequent the bars of any city including our own have felt the sting of rejection. At least the ladies here don't use indelible ink.

© 2014 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Octopus prefer mating to be rough and tumble... with eight arms, what else would you expect?

This document maintained by Dr. Bill Bushing.
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