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Dive Dry with Dr. Bill

#559: Munching... And Defending Your Life

I hate to keep repeating myself but, as a former classroom teacher. I've learned that repetition is often necessary to drive a point home. On occasion I asked my high school students to write a biological term on the chalkboard (yes, we used chalk way back then) 100 times so they just might get it. So I'll repeat myself here, too. Two of the most important functions of any critter (land or sea) are munching and mating. Munching allows the individual to live, grow and eventually do the other "M" word which allows the species to continue. Even human beings (aka Homo sapiens) are driven by these two important functions. To be a biologist almost requires being gluttonous and libidinous... unless you're one of those who sits in a lab all day looking at critters preserved in formaldehyde. No thanks.

As my readers know, I focus my underwater imaging and my columns on these two important functions. To take a pretty picture of a nudibranch (colorful shell-less snail) may elicit "ooohs" and "aaahs" from those who view it, but video footage of critters involved in actual life or death behaviors is far more interesting to me (and I hope to you as well). That's why my very first DVD was titled "Munching and Mating in the Macrocystis" (giant kelp). Although respiration is another critical function, I didn't think anyone would buy a DVD that focused on "Breathing in the Macrocystis." After producing 24 DVDs in the past decade, I'm once again focusing on these behaviors in a new high definition video about the Night Shift. That has required doing a lot of diving under the light of the moon. Being one possessed of good sharp canines, this is preferable to daylight anyway!

As an ecologist, I know that to truly understand any ecosystem like the kelp forest, one needs to not only do thousands of dives in them... but to spread those dives over the 24 hour cycle. Critters like the sheephead, blacksmith and garibaldi that are active during the day retire into the nooks and crannies of the reef to sleep (and avoid nocturnal predators like seals and sea lions). Those that hide during the day including round stingrays, worms, lobster and crabs come out at night. It's a whole different ball game after the sun sets. During summer I usually do most of my dives at night to film these critters while the drive home is reasonably warm. I'd love to get up about 4:30 AM to film the critters that are out and about before the sun rises... but my alarm clock doesn't have settings for that early.

This summer I've had a lot of fun filming southern kelp crabs (Taliepus nuttallii)... the beautiful, deep red decapods that come out of hiding at night. They are a great species to film because their behavior usually consists of munching or mating... and occasionally both at the same time! They feed on seaweed and also scavenge so the munching part isn't all that exciting... not like a cheetah chasing down an impala on the African savannah. By the way, did you know a cheetah can do 0 to 60 in three seconds... much faster than my Toyota Tercel (but who needs speed on the L.A. freeways?). However, crab mating is far more interesting as they have their own version of the Kama Sutra and the male drags the female around afterward, presumably to prevent other males from partaking and thus ensuring his genes will be passed on.

On a recent dive I had the opportunity to film another behavior that is also critical to survival. I call it "defending your life" (although it bears no resemblance to the movie starring Albert Brooks and Meryl Streep). Since munching is such an important function of any species, avoiding being munched is pretty critical as well. And many marine critters have developed elaborate mechanisms or behaviors to prevent becoming dinner (or breakfast or lunch). I do plan on creating future episodes of my cable TV show about this. For those of you too cheap to buy my DVDs, I've posted almost all of them on my YouTube channel (drbillbushing) so you can watch for free... and help cure your insomnia.

Getting back to the dive, I found a male southern kelp crab munching on a tender seaweed salad and followed him as he crawled around the bottom. I ended up capturing about 13 minutes of video which is rather unusual since they often duck into a crevice or under a rock when I shine my video lights on them. You do remember my column about negative phototaxis... moving away from the light? This one didn't seem to find a nook or cranny that suited him.

I was following it from the bottom up the face of the rocky reef when suddenly something entered my video frame from stage left. It took a second to realize that it was a hungry octopus. The octo grabbed the crab with its eight arms, and its mantle enveloped it. Then, just as suddenly, it made its exit. It wasn't until I edited the video footage that night that I realized what had happened. Now the octopus was probably a bit overly optimistic since the crab was about the same size, so I questioned how much success it would have injecting its venom to subdue the tasty crab.

By slowly stepping through the video frames, I saw that the octopus jerked a bit after it captured the crab. As it retreated, I could see the crab's left claw withdrawing from an extended position. Apparently the kelp crab had defended its life with a pinch to the soft mantle of the octopus and would live another day to munch and mate (oh, and breathe). Back in October of 2006 I was diving at China Point when I spotted a larger octopus dragging a southern kelp crab along the bottom. I followed it as it climbed up over the reef, dragging the crab into a cavelet where it finished off its meal. That crab was not so successful in defending ITS life!

© 2013 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 attacking southern kelp crab and retreating after being pinched; octopus that didn't defend its life successfully.

This document maintained by Dr. Bill Bushing.
Material and images © 2013 Star Thrower Educational Multimedia