Dive Dry with Dr. Bill

#207: Eight Arms to Hold You

All my regular readers know that I tend to place a strong emphasis on "munching" and "mating" in my columns, cable television show and DVD's. As a marine ecologist, my professional function is to study the interactions between organisms. These two interactions are among the most important to every species... with avoiding being "munched" and breathing playing important roles too, of course. Now given such possibilities, how many of you would rather be a taxonomist deep in a museum lab who counts the number of rays in the caudal fin of a fish or the ratio of the antenna to body length in an invertebrate?

Of course we need this kind of research, and before the era of SCUBA marine biologists often had to be content with examining pickled specimens from expeditions in remote regions. They had to distinguish between species based on these metrics or countable characteristics of their specimens since they had little else to go on. For most "well-behaved" species, it is the ability to mate with one another that really defines whether they are the same species. Humans are all Homo sapiens whether they are black, yellow, red, brown or white. For myself, I prefer to continue earning the title given me by divers from as the king of underwater "pornographers."

One recent July day I was on my third dive off Scuba Luv's dive boat, the King Neptune, at Torqua Springs. Due to the high level of silt on the rocks at this site, I usually don't expect to see much of interest there. However, I was quickly surprised when I observed and filmed an event I'd never witnessed before! I noticed two octopuses close together. I had startled them and they had separated. Once they realized cephalopod creole was not on my mind, one moved back towards the other and I quickly surmised that I had become a voyeur watching these two shameless octopuses mate right in front of my eyes... and camera.

This amazing activity continued for quite some time... and I never once witnessed the male take a little blue pill. It was very difficult to follow the behavior since I was observing it through a 1/2" viewfinder. When I returned home to view the footage, I still couldn't "make out" (so to speak) much of the interaction. There were just two many arms... er, tentacles... flailing around. The male's eight tentacles seemed to intertwine with the female's eight. I've observed hostility between octopuses, but this was a much more gentle interaction. To verify I had actually observed mating behavior, I sent the footage to Avalon's own Dr. Eric Hochberg at the Santa Barbara Museum of Natural History. As a cephalopod expert, he confirmed that I saw what I thought I saw, and was not simply under the influence of nitrogen narcosis... or wishful thinking.

My Internet research for this column was very revealing. I knew the male octopus uses a specialized arm, usually the third one on the right side, called a hectocotylus to insert packets known as spermatophores, which contain millions of sperm, into the female's mantle cavity. Two researchers at the Field Museum in Chicago ("my kind of town") noted that a male of our common local species had a very enlarged arm while attempting to mate with a female in his tank. Further investigation showed that the male was capable of increasing blood flow into a structure known as the ligula on the tip of this reproductive arm and thereby having an erection, the first documented in an invertebrate. It is believed this may aid in depositing the spermatophores, and possibly even allow the male to scrape sperm from other males out of the female's cavity to better ensure he is the successful mate.

Our two-spot octopus often feeds during the day. The ligula is white, and has no chromatophores to allow it to change to match the surroundings. It is believed the ability to enlarge the ligula only during mating encounters is a survival mechanism. While in the open feeding, a large white arm would make the males easy targets for potential predators. Therefore it is normally very small in size... until just the right moment.

Once mated, the females of some species can keep the sperm alive for weeks. Although some species may lay up to 200,000 eggs, our local two-spot octopus is thought to lay about 500. Females of some octopus species lay their eggs in strings attached to the ceiling inside their holes, keep them clean and spray them with jets of water to increase oxygen flow. Others, probably including our species, lay their eggs and attach them individually to the bottom. Eventually the eggs hatch and in most species the young drift with the plankton until they settle out.

Apparently mating in octopuses has serious consequences! Often females die shortly after their eggs hatch since they do not eat during the month or so they care for their eggs. Of course if humans had 500 to 200,000 young it might be the same for our species. It is said the males live only a few months after mating. Our local species lives for a total lifespan of 12-18 months.

The same Chicago researchers observed a female reject a male that attempted to mate with her, so the female has some control over the selection of her mates (just like the human females I encounter). I could use eight tentacles... er, arms... myself. Maybe I could finally capture a lovely mermaid as a permanent dive buddy. However, I'm not about to die for love so perhaps I should be happy to remain celibate!

© 2006 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays. Please help me climb out of self-imposed poverty... buy my "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles" or "Gentle Giants: Giant Sea Bass" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!

A two-spot octopus in the open and the male "pouncing" on his mate;
the tangled web of sixteen arms as the two complete their shameless tryst!

This document maintained by Dr. Bill Bushing.
Material and images © 2006 Star Thrower Educational Multimedia