Dive Dry with Dr. Bill


My readers will probably be glad to hear that my new "number #1 dive buddy" has wandered off into the depths with another diver before we even got a chance to really pursue our relationship. I guess some ladies are as fickle as our own garibaldi and giant kelpfish men folk. I'm more like a black sea bass or a butterflyfish. At least I've rediscovered the reason I prefer diving solo... I can always count on my pony bottle! Bad for me, but good for you because it means that my focus on "mating" will probably intensify in future columns. In fact, I'll start with this column and a return to the weird and wacky... our marine wabbits, more commonly known as sea hares.

In a previous column I wrote about the more common sea hare, sometimes called the California brown sea hare (Aplysia californica). Today's column will be about the less common (at least in our dive park) California black sea hare (Aplysia vaccaria). The day I observed these, they were truly "happy bunnies" doing "what comes naturally" (and I don't mean munching).

The black sea hare is probably the world's largest snail. They reach lengths of over 30" and may weigh as much as 35 pounds. By comparison the brown sea hare reaches a maximum length about half that and weigh under 10 pounds. One might consider the black sea hare to be the Jose Conseco, Barry Bonds or (dare I say it) Arnold Schwarzneggar of marine snails, but the "steroids" actually come naturally from the algae they munch on. Hard to believe one can build such bodies just by eating "salad."

These sea hares are known from Morro Bay to Bahia de Los Angeles in Baja California. Although referred to as the black sea hare, their large bodies may be a dark reddish brown to black, with speckled white patches of varying intensity. Although they are relatives of the nudibranchs, these opisthobranchs have a small internal shell. It doesn't offer any real protection, but then what fish can swallow one of these behemoths? They also lack the defensive purple ink of their smaller relatives.

Black sea hares are reported to feed almost entirely on the feather boa kelp (Egregia). If I were a marine vegetarian, this tough kelp would not be my number one menu item. Of course there probably isn't too much competition for this food other than smaller "snails" like the top snails or occasionally abalone. Sea urchins will also eat drift feather boa chunks, but they have some tough "teeth" to chew it up. It has been reported scientifically that the smaller tentacle-like structures on the head are used to sense food, while the much larger rhinophores (which give them their wabbit-like appearance) may be used to detect currents and obstacles in their path.

Like its smaller brother/sisters, this sea hare is hermaphroditic and has both sex organs functional simultaneously. This greatly facilitates finding a mate since any other sea hare they meet at the local kelp bar will be suitable for mating. Despite my recent setbacks, I'm not ready to utilize that strategy in my own approach to mating! The sea hares seem to like to carry things to the extreme. They are rarely satisfied with just a single (fe)male mate. They usually form mating circles in which several sea hares become lucky lottery winners all at once.

The mating circle I encountered consisted of four individuals. I discovered them after following a black sea bass a few weeks ago. They are so dark, I didn't see them initially. What drew my attention was the football-sized egg mass that looked suspiciously like Mamma Mia's Day Old Spaghetti from Antonio's. Each spaghetti-like strand had numerous eggs embedded in it. Carl Sagan would probably say there were "billions and billions" of them in the growing egg mass. Of course many will be eaten as eggs, as larvae once they hatch out, or as young adults that are a suitable mouthful for any predators who encounter them. Once they achieve full size, I would assume they are pretty safe from being munched.

In researching this column (you think my brain already contains all this?), I discovered that sea hares use chemical signals to attract mates. Many animals (including humans) have sex pheromones which attract potential mates. In humans perfumes and scents are often related to our own pheromones (I'll have to work in the lab late tonight to improve mine... better living through chemistry). In the sea hare, these chemicals are released during egg laying and may be carried some distance in the water drawing other individuals to join the orgy underway. Our two local sea hares, the brown and the black, use different sex pheromones so they don't attract one another. That's good given the substantial size difference between them (hmmm... not much different than some humans)!

After I wrote this column, I was shocked recently to find a "mating circle" that included both the brown and the black sea species! Perhaps an interesting scientific first? I did notice that the brown and black sea hares were only mating with their own species. However, the two egg masses produced were laid practically on top of one another. I have revisited the egg masses several times since they were laid and there seems to have been very little predation. This leads me to hypothesize that sea hare eggs of both species employ some form of chemical defense that makes them unpalatable to fish and other potential munchers. Some have said my cooking has the same quality.

© 2005 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. Buy my "Munching and Mating in the Macrocystis" DVD so you can take Dr. Bill home with you... we'll both be glad you did!

(Top) Black sea hares nuzzling one another in mating circle; (bottom) black sea hare egg
mass, egg masses from both black and brown species of sea hare.

This document maintained by Dr. Bill Bushing.
Material and images © 2005 Star Thrower Educational Multimedia