Dive Dry with Dr. Bill

#354: In the Dark About Mating

Regular readers of this column know that I have a few "icons" I admire and one that I've semi-consciously patterned my life after. That particular one is Edward F. "Doc" Ricketts, the role model for "Doc" in John Steinbeck's Cannery Row and the sequel, Sweet Thursday. Doc and I share many characteristics... he was an avid "student" of marine life, a connoisseur of interesting women, a lover of beverages alcoholic, and a very poor businessman who let his bills remain unopened assuming that if he did so, they wouldn't have to be paid. Fortunately, he had Steinbeck as a patron and John had to bail him out financially a number of times. That is where we differ! Oh, and he didn't like to get his head wet and even wore a sou'wester in the shower!

Back in 1941 "Doc" and John chartered a Monterey sardine boat and made an extended scientific collecting trip through the Gulf of California, perhaps more commonly known as the Sea of Cortez. Their vessel was provisioned with food, collecting equipment and another essential... plenty of beer. As a SCUBA diver, I cannot consume the mass quantities of that ambrosia to the extent "Doc" and John did, or I'd risk serious and potentially life threatening dehydration! Of course even their considerable stock was depleted quickly... giving them the opportunity to discover the many delicious Mexican beers.

These two close friends were fond of philosophizing, with Ed being a particularly seminal thinker. Unfortunately Ed's writing skills were not sufficient to convey the beauty of his philosophy on life. Fortunately, John's were and we are blessed with a number of his novels that beautifully detail their collective thoughts. John waxed especially philosophical in The Log from the Sea of Cortez, the story of that adventure. One line from that book was "It is advisable to look from the tide pool to the stars and then back to the tide pool again."

As an underwater videographer, I generally spend most of my time underwater looking down towards the bottom. For that reason I always miss the great white sharks, manta rays and whale sharks (in tropical waters) that pass overhead. Recently I've been taking advantage of the still toasty waters to film the "night life" in our dive park. Okay, it's not quite like the Chi Chi Club or karaoke at El Galleon, and I'm usually the only one in the dive park, but the subjects I encounter are well worth it. On one dive during a full moon, I happened to take Steinbeck's advice and look up. I was pleasantly surprised to see a totally new subject to film!

Caught in my high intensity video lights were two polychaete annelids (marine worms) wriggling upwards through the water column. Nocturnal spawning by worms during full moons is common in a number of species. These seemed to mistake my lights for the moon and swam swiftly towards them, making the worms difficult to film. These polychaetes were extremely vigorous in the twists and turns of their bodies as they rose through the water column. Since this made it hard to follow them in the viewfinder, I hypothesized (scientific word for educated guessing) that it would also make them elusive targets for any nocturnal predators. To swim in open water like this during the day would certainly have made spawning a deadly act.

Why would worms spawn by swimming up to the surface? I would think most species would prefer to just snuggle into a comfy burrow with a bottle of wine to enjoy a little privacy as they consummate the second most important "M" word (Munching being the first, of course). By rising to the surface under cover of darkness, the worms are able to spawn in the open where their fertilized eggs will be able to drift in the surface currents to far off destinations. Much easier to start out with an "empty nest" and not have to provide weeks or months of child care... or pay for their "education."

What triggers these polychaete worms to spawn? Obviously they need to do it at the same time, or some lonely worm might find itself mate less when he or she gets the urge to continue the species. I know the feeling! Signal cues are necessary to ensure enough of the species participate. Although worm spawning is often associated with full moons, they are known to spawn during new moons as well. These lunar phases are times of the highest and lowest tides. If I were a worm and had to swim to the surface, I'd want to do it at the time of lowest tides so I had to exert less energy. Of course this is just another hypothesis, and after checking the tide charts for the dates and times I dove, the tide levels ranged from low to high. Apparently I'll have to discard that hypothesis and try something else that meshes with the facts! Scientists have to be flexible and adjust their thinking when the facts prove them wrong. I wish more politicians employ that objectivity!

Temperature has been shown to be another factor in triggering mass spawning. The waters at Casino Point have been pretty toasty (for southern California, not for "warm water wussies" like tropical divers) this month. I doubt temperature alone triggered these critters. Other scientific studies have shown that polychaete worms, like many other species including our own, use chemical signals known as pheromones to trigger mating. Of course these chemical signals must be specific to each species, or the worms would be joined by crabs, squid, fish and maybe even a few divers! My sense of "smell" is pretty limited, especially underwater, so I wasn't aware of any exotic (or erotic) scents myself.

Scientists have studied a range of chemicals in worms that might serve as sexual pheromones. Steroids were considered, but found not to stimulate spawning. I guess the female worms are not fond of overly muscled monster males. Interestingly, volatile organic substances derived from crude oil did trigger the mating urge in some worms. Uric acid was found to stimulate other worm species. Yuck.

Of course once the boys and girls reach the surface, they still need to find one another unless they are broadcast spawners casting their gametes into the water and hoping, like lottery ticket purchasers, that they will get "lucky." Even broadcast spawners need to increase their odds by getting close enough to better ensure fertilization. Some worms have solved this issue by adopting the same technique as that of the fireflies I used to catch during my youth in Chicago... and a number of marine critters that live in the perpetual darkness of the deep ocean. They are bioluminescent and generate "cold light." Often it is the male who flashes to attract the female. Were the female to do so, she might draw the attraction of a predator intent on doing the Munching "M" word rather than the Mating one. Obviously that would not do. Better to risk sacrificing a few males rather than the ladies... a form of chivalry I guess, but not one I'd participate in!

© 2009 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 and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. 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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The polychaete worms I observed in the act of rising to the surface to spawn,
and on their return to the safety of the rocky reef.

This document maintained by Dr. Bill Bushing.
Material and images © 2009 Star Thrower Educational Multimedia