Dive Dry with Dr. Bill

#200: Mating Can Be Deadly

Hard to believe, but this is the 200th "Dive Dry" column that I've written. In honor of that benchmark, I'll focus my attention once more on one of my favorite subjects. While mating is one of the fundamental activities of any species, it can also be one of the more dangerous activities a species undertakes. Over the past 25 years the threat of HIV and AIDS has certainly reinforced that understanding, although monogamy can certainly eliminate almost all of that risk. Even for humans, this is not a recent phenomenon. In days of old, sexually transmitted diseases including syphilis were a serious threat before modern medicine. Even such common diseases as measles were transmitted when European explorers visited the New World where the native humans had no experience with, or immunity to, such infections. In the early days of our species even childbirth posed serious dangers to the mother.

Fortunately my "mating" days are over (sigh) so I needn't worry about such things. However for many other species that occupy this planet, mating remains a potentially dangerous necessity if one is to continue the "blood line" or species. I was recently reminded of this on a dive with buddies Mina and Mark at Yellowtail Point near Empire Landing. The visibility was poor thanks to groups of munching bat rays hammering the sandy bottom nearby, a frequently encountered situation in our waters this time of year. Despite the murky conditions, I noticed an interesting assemblage of species to illustrate this point.

Many gastropods, or snails if you prefer, have been mating and producing large egg masses in our waters. 'Tis the season, at least for them (sigh again). Now snails generally do everything at... well.. a snail's pace. Mating is certainly no exception. Some species like the black sea hare may form mating circles that continue for several days... without benefit of Cialis! Sounds like a good subject for medical research if you ask me. However, this coziness is one of the reasons why mating can be deadly.

My "find" that day was a large knobby or giant-spined starfish (yes, I know... I should say sea star). At first it appeared to be nothing of significant interest until the dust settled and I could see what it was resting on. Beneath this sea star was a group of mating Kellet whelks, a fairly large species of snail common in our waters. The "urge to merge" had brought these snails together. Of course when you concentrate a potential food source, like these "escargot," a predator can have a field day if it happens upon them. And, yes... the knobby sea star is a predator on such snails.

I carefully turned the sea star over, not wishing to dislodge its potential meals... or to disrupt the mating of the Kellet whelks for that matter. In addition to the whelks, there were several wavy top snails in the mix. The sea star had a two course meal on its "plate." I have no idea why the wavy top snails were mixed in with the Kellet whelks. It certainly wasn't someone's purpose to spread a gourmet buffet before the sea star. Perhaps the Kellet whelks use a chemical attractant, known scientifically as a sex pheromone, to draw one another closer. You know, like a woman's perfume or a man's after shave... or, as has been scientifically demonstrated, human sweat (ugh). If so, maybe it is close enough to attract the wavy top snails as well. The best sex pheromones should only attract members of your own species (or a potential dinner in some cases), but who's perfect?

So our mating Kellet whelks, and the wavy top snails foolish enough to join them, had drawn the attention of the predatory starfish. If snails mated at the speed of the human male, this would all have been over in seconds and the Kellet whelks could disperse quickly for greater safety. Their preference for a more leisurely interaction most likely proved deadly for some and perhaps all. The urge to reproduce is no good if one gets munched on in the process!

Makes me wonder if maybe other forms of reproduction aren't the safest bet, at least for marine critters and species other than our own. Some, like sea urchins, are broadcast spawners which release their gametes all together and rely on fertilization in the surrounding waters. The odds are slightly better than winning the lottery, but the adults are much safer. Then there are those that reproduce without "benefit" of sex. Sea anemones and others often reproduce asexually by splitting into two. Instead of two making one (or more), one makes two.

I filmed this interaction for several minutes. While doing so, a garibaldi pushed its way into view of my camera. It had been attracted by a delicacy, an hoerdourve of great appeal but rarely tasted I assume. By turning over the starfish, I had revealed its many soft tube feet used to hold on tightly to its prey. The garibaldi began nipping at the tube feet until I finally chased it away (it was quite persistent). This was truly a case of "munching" and "mating" in which a small food chain emerged and the dangers of both activities were clearly illustrated!

© 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!

The knobby star right-side up and its buffet of mating Kellet whelk snails
and wavy top snails held tightly near the mouth by its tube feet

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