Dive Dry with Dr. Bill

#331: Dancing in a Hula Skirt

I was sitting at my computer on a Sunday afternoon, finishing up my 15th DVD ("Greenlings and Gobies of SoCal") when the phone rang. The call was from "Big Dave" Brown who was on his boat in Avalon Bay. He said his daughter Lana had brought something into the boat with her fishing pole and he had no idea what it was. I asked for a description, and from it I thought she had captured a Pyrosoma, an unusual orange open water tunicate I've seen a few times in our waters. I asked if he could bring it up to the house so I could confirm that.

Dave called when he, Lana and her brother Lars arrived at the house, and I went down with a camera to see if I could identify the critter. I looked into the bucket and there "she" was, all dressed up in an orange hula skirt dancing to music only "she" could hear. No, it wasn't my long sought after mermaid, although it did trigger thoughts of diving warm waters in Hawaii... or the Philippines! In fact, I wasn't sure exactly what this orange-colored jellyfish-like critter was. I went back upstairs to fetch my copy of Wrobel and Mills' Pacific Coast Pelagic Invertebrates: A Guide to the Common Gelatinous Animals and my high definition video camera. Before I reached the bottom of my condo stairs, I had determined it was probably a siphonophore of the order Calycophora. The only species pictured in the book was Physophora hydrostatica. Don't worry, that's all Greek to me as well.

I filmed the unusual critter so I could use the footage to solicit an ID from a specialist. Lana and Lars used a small net to capture the critter for a closer look. Dave wisely cautioned her about touching the net in case it could sting. I was so focused on filming the unusual thingie that my mind wasn't grasping the fact that siphonophores are known for their powerful stings. One member of this group is the notorious Portuguese man-of-war, which my mother had a painful close encounter with when we lived in Florida many decades ago. I have also encountered two other relatives, Apolemia and Praya, in our waters and received a good sting from the latter when its tentacles brushed over my face as I filmed it a little bit too "up close and personal."

Both Dave and Lana were concerned about the little critter's survival, and wanted to return it quickly to the water (kudos to both of you!). I went back upstairs and Googled both the order Calycophora and the species name listed in the book. Through my search, I discovered that there may only be one species in the genus Physophora. Lana's specimen was bright orange with a touch of pink or violet, and didn't look like the image in the field guide. However, I learned that this species could appear in a range of colors including orange, pink and violet. I also discovered it had a common name, the hula skirt siphonophore!

This species may reach a total length of 16 inches. It is designed on a modular basis with different body structures specialized for swimming, feeding or movement. Half of the body length is composed of the gas-filled float and the swimming "bells" that propel it. Attached to the base of the bells are the finger-like "dactylozooids" which have the potent stinging cells or nematocysts common in all members of the Cnidaria (formerly Coelenterata) including jellyfish, sea anemones and corals. Trailing beneath them are a series of thin tentacles that can change length significantly.

The hula skirt siphonophore typically swims about slowly with its tentacles extended to feed on zooplankton (animal plankton). Its average speed has been clocked at a blistering one foot per minute, although Lana's specimen seemed to exceed that thanks to rapid pulses of its swimming bells. Scientists have determined that their stinging nematocysts are specially adapted for capturing small planktonic crustaceans like copepods rather than soft bodied organisms like fish larvae. The float at the top adjusts the critter's buoyancy by changing the amount of gas in it, just like my trusty BCD. There is a pore at the bottom that can release gas if necessary, and a special gland that can increase it.

My research produced conflicting results regarding the geographic distribution of this species. One source stated it was found in the Pacific and Arctic Oceans, while others placed them in the western Atlantic, off Brazil and in the Mediterranean. Some referred to it as "subtropical," yet it is seen in the Arctic. This, and the reported depth range of 2,300 to 3,300 feet, hardly seems "subtropical" in my eyes. Brrrr! So why was it collected right here in Avalon Bay if it is a deep water species? One source mentioned that it is occasionally seen near the water's surface off central California, but never in significant numbers. My guess is that this individual may have been brought to the surface during a period of strong upwelling of cold, deeper water.

I was also interested to discover that the hula skirt siphonophore was initially collected and named on the HMS Challenger Expedition of 1872-76. Our own space shuttle Challenger was named for this vessel. The ship's globe-circling, nearly 70,000 nautical mile voyage is considered to be the first modern oceanographic expedition. Looking at the route taken, it almost looks like the HMS Challenger was captained by the same man who navigated the Exxon Valdez! Researchers on board collected more than 4,000 new species on this adventure. In my undergraduate years at Harvard, I occasionally sat in the library at the Museum of Comparative Zoology reading the published accounts of this expedition. The dusty volumes were sitting there right on the library shelf. So for me this discovery by Lana, Lars and Big Dave included a personal connection that spans more than 40 years. Thanks for the new discovery and reawakening some old memories. And thanks again for caring about this critter's survival by returning it to the water.

© 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!

Color enhanced images of the hula skirt siphonphore in Dave's bucket and an image by
noted underwater photographer Norbert Wu with the "modular" body parts labeled.

This document maintained by Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia