A few months ago I was diving Italian Gardens, looking for the black sea bass. They were playing hide-and-seek with me so I decided to see what else I could find. I consider this dive site a rather boring one if the bass aren't present, but I was in for a surprise this time. And I like surprises! As I nosed around on the rather featureless gravel bottom, I noticed a few arms sticking out of the sand. No, this was no crime scene... I hadn't discovered Natalie Wood's remains. The tiny arms sticking out of the bottom numbered five rather than two and they were trying to capture food to carry down to the critter's waiting mouth.
What I had discovered was the brittle star Ophiopsilla californica, or at least its long slender arms. This relative of the starfish and sea urchins remains buried in sand or mud bottoms with only the arms exposed. These arms grab organic matter and probably plankton as it drifts by. The unusual thing was that this species, which has no common name, is not supposed to be here! It is known only from central California based on the field guides I consulted. Of course it is easy to miss them unless you look closely, so research divers could easily pass right over them and not record them during casual surveys.
Although unusual, I had only discovered one individual at this site. Perhaps a young larval brittle star drifting down in the current from up north just happened to make it as far as Catalina and settle here. It wasn't until I discovered entire fields of them in the sand at the base of Bird Rock that I really got excited. Yes, I know, it doesn't take much... imagine how I'll react when I finally meet my mermaid! Everywhere I looked at this deep depth there were brittle star arms sticking up out of the sand. This proved Ophiopsilla had successfully established populations here on Catalina, well outside their reported range!
Like their relatives, brittle stars exhibit five-part symmetry. Their bodies are star-shaped with a round central disk that contains the digestive tract. They are called brittle stars because their arms can break off easily. This is one of their defense mechanisms. If a fish attempts to eat them (as many do, especially sheephead), the arm breaks off and the rest of the brittle star scurries off under a rock or buries itself in the sand. The fish gets a paltry meal and the brittle star escapes and regenerates the lost arm just like their starfish (er, sea star) relatives.
At the base of each arm are slits that open into internal pouches called bursae. These play a role in breathing and in the release of sex products or brooding of the young. Good thing human lungs don't serve this dual purpose, although for some shallow males a lady's "lungs" may be a factor. Readers, please keep in mind that I am a "deep" diver in this respect, and look for characteristics like a large mind instead. In many brittle star species, males release their sperm, and females their eggs, into the water column where they are fertilized. The young develop into larvae that drift with the currents. This is a risky reproductive strategy due to all the fish and other predators feeding on the plankton. Species using this strategy usually produce large numbers of eggs to ensure some will survive. In other species, the female produces fewer eggs which are fertilized and retained in her bursae. The eggs hatch into tiny juvenile brittle stars that eventually emerge from the pouch and begin life without entering the horrendous world of the plankton.
These two reproductive strategies have quite different consequences. The brittle stars which produce drifting larvae ensure that their young may colonize new habitats or ones where the species is already established. In the first case, the species has dispersed to new locations. In the second, they have ensured that new genetic material will mix with that of the already established individuals. Don't want too much inbreeding... fresh genetic material usually improves the health of the population. Those brittle stars which brood their young ensure higher survivorship, but must rely on other mechanisms to disperse. One way is by drifting on detached kelp holdfasts as I discovered in my early scientific investigations here during the 60's and 70's.
While researching this column, I was surprised to find how little information is available on the brittle stars of California. Their distribution, ecology and other behavior does not appear to be well known. I find them very interesting little critters and had assumed other scientists did too. One of my mentors at Harvard, Dr. H. Barraclough "Barry" Fell, was a noted specialist focusing on echinoderms including brittle stars. He later became much better known for his investigations into the exploration of North America by cultures such as the Vikings (and not the ones from Minnesota) and the Egyptians who he claimed ventured to our continent well before Christopher Columbus. Of course there isn't much grant money available for studying brittle stars, and even scientists are prone to say "show me the money!" I'd appreciate it if someone would point me in that direction! And I'm not referring to lottery tickets (unless you can give me the winning numbers).
© 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!
The sand dwelling brittle star Ophiopsilla
Italian Gardens and Bird Rock.
This document maintained by
Dr. Bill Bushing.
Material and images © 2005 Star Thrower Educational Multimedia