Dive Dry with Dr. Bill

#206: Bat Stars Courtship

This week I thought I'd return to a theme that makes all our hearts go pitter patter. That's right, mating. Now before my readers accuse me of having a deviant mind with thoughts deemed socially unacceptable (at least by those who only express them behind closed doors), let me say a few things about this subject. I've spent years observing underwater sex, at least between marine critters. Since I rarely observe mating in marine mammals, it is very rare for me to film something that would trigger a human's prurient interests. Let's face it, sex among many marine species borders on boring... at least for me... but it is critical for their survival as a species.

In years past I had to travel to more northerly dive sites like the four Channel Islands off Ventura and Santa Barbara to observe many of the species I now find in the colder waters at depth around our own island. "How deep?" you ask. Well from now on I'm just going to answer "to the bottom" and leave it at that. I wouldn't want other divers to attempt to duplicate some of my dives. They should just "Dive Dry" in their easy chairs with no wetsuit or cold water required and just enjoy the interesting things I bring back from my dives to inform, and entertain them... and you.

The subject of this column can be found well within recreational depth limits. In the northern Channel Islands I see them at fairly shallow depths, but must search for them in the colder waters around Catalina. I'm referring to the bat starfish, or if you wish to be "correct" in this P.C. world, the bat sea star. Like most sea stars, this species usually has five arms but they are webbed in between like a bat's wing. Some sea stars show great conformity with each individual looking like a clone of the others. Bat stars have greater genetic diversity, expressed in the form of an array of attractive colors and patterns. For this reason they make excellent subjects to film.

I descended along the anchor line at several Catalina dive sites recently (Sea Fan Grotto, Empire Landing Quarry and Blue Car Wreck) to film these attractive "stars" for my next DVD. At the Quarry I found the bat stars were not randomly scattered across the sandy or muddy bottom. They were aggregated in groups. Now individuals within a species aggregate under differing conditions and for different reasons. Like baitfish they may group together for defense against predators. Predatory fish like yellowtail or barracuda may group together and hunt in teams to better ensure success. And, of course, many species have to group together for that most divine "porpoise..." reproducing the species.

I filmed the bat stars, capturing as many colors and patterns as possible. In true ecumenical spirit there were 5-armed Christian bat stars and a few 6-armed Bat Stars of David. And there were some that had the tips of their arms bitten off by predators, and others in the process of regenerating lost limbs. However, the thing that captured my attention were the pairs of bat stars with their arms raised towards one another. No, they weren't offering a toast (what marine critter drinks alcohol?).

When bat stars get "the urge," they approach one another and raise their arms towards one another. Although they don't always touch one another, this does enable them to chemically sense potential mates by taking in water through the tube feet on their arm tips. Now I have no clue what scent a bat star is looking for to trigger mating. I'm going to assume they know and that's all that matters.

Although only a small percentage of the bat stars in these aggregations were "sniffing" one another, I have a feeling I'd see more such activity if my tank was much larger, allowing me to stay under longer, and I wouldn't be affected by nitrogen narcosis at that depth. Hmmm... maybe that's why I've never seen a marine creature with a cocktail. They're all narc'ed! Why the boys don't even have to buy the girls a drink to get them in the mood.

I couldn't see any pattern in their mate selection. Red ones courted with blotched ones, purple ones with orange ones, and beige ones with lavender ones. After all, they're all the same species so it shouldn't matter. I did feel a tinge of sadness as I edited the footage back home. Labor Day heralds the approach of fall... and winter. We all know that spring and summer are when a young marine critter's fancy is aroused. Much of the wonderful mating behavior that I've observed the past six months will be fading away. Fortunately "munching" goes on all year 'round so I'll still have one of my favorite subjects to film and write about in the coming months!

© 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!

Bat star aggregation and courting couples doing their thing... not much for us humans to get excited about

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