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Dive Dry with Dr. Bill

#360: Sailor "Home" from the Sea

Since the early 1980s, my life has been dependent on computers. I'm either diving with one to film the undersea world, or editing the resulting video on my desktop computer to create new episodes for my cable TV shows and extract stills for my columns to share this fascinating world with you. Last Sunday night I was on my Dell Vostro 400 desktop when suddenly the screen froze. I've had trouble with this system since I purchased it 18 months ago, but was hopeful after four different motherboards and four different video cards, it had finally begun to function properly. Michael Dell and I had practically become penpals since I went directly to him after the first few problems were not satisfactorily fixed by his tech support gurus. This time when I tried to reboot, the system was obviously dead... probably due to a total failure of the FOURTH motherboard! Grrr!

With my primary work tool down and out, I decided to try something completely different. I took the book "Shanghai Girls" (don't worry, it is G rated) out onto my front deck to read in the warm sun. I got through about 15 pages before my head slowly sank to my chest. I awoke suddenly, a bit disoriented, to hear a woman's voice on my telephone answering machine. I didn't know who had called, but she said she had collected a strange blue jellyfish out at Pebbly Beach. I told her to bring it up and I'd identify it. When she appeared, it turned out to be Tina Quinn (sister of my former Toyon student Steve) and Cindy Reinhart.

As I suspected from their description of the beast, it was none other than Velella velella... commonly known as the blue button "jellyfish" or by-the-wind-sailor. I've seen them here before, sometimes in the hundreds or thousands when they'd land on our local beaches. Although a rare event, I was sure I knew "all about" this unusual creature and began to shower Tina and Cindy with my "knowledge." However, when I started researching Velella for this column, I found out how wrong I was and how much our knowledge of them had changed since I first studied them nearly 40 years ago. It reminded me that the "facts" I taught in my astronomy class back then have also been largely replaced by new scientific discoveries. Our understanding of the Universe does indeed change over the years.

When I first studied Velella, it was believed to be a siphonophore like the hula skirt siphonophore I wrote about earlier, and the Portuguese man-of-war that severely stung my mother when we lived in Florida. I told Tina and Cindy about it and its potential to deliver a sting. However my research revealed that it is now considered to be an open water or pelagic hydroid, a relative of the siphonophores, corals and jellyfish. Its stinging cells, known as nematocysts are not capable of penetrating human skin, or at least the toxins do not affect us, so they are safe to encounter in the water.

When classified as siphonophores, they were thought to be a complex colony of specialized individuals. Some were adapted to feed ("munching"), others for reproduction ("mating") and a third type with stinging cells for defense. Scientists now realize that "they" are a single hydroid polyp rather than a colony of individual critters, although some sources refer to them as a hydroid colony. I guess further study may be needed! Of course according to Occam's Razor, the best explanation is often the simplest one. The individual components may be specialized however, and it is apparent that each polyp is connected to a common digestive gut so they all share any food captured.

Velella velella usually has an oval shaped float from which the hydroid polyps hang, and a sail-like structure that catches the wind and moves them about at the ocean's surface. This one was young, and had a circular float about the size of a dime with no sail on it. They are a beautiful blue to purple in color. These hydroids are carnivores feeding on small prey including fish just below the water's surface. The polyps do not extend very far into the water column like those of many true sea jellies, and they do not submerge below the surface. In turn they are munched on by predators including pelagic nudibranch snails like Glaucus and Janthina.

Velella is found in the Pacific Ocean, usually well offshore in the central part of that huge ocean basin. They are also present in warm and temperate waters globally including the Atlantic and Mediterranean. Wind patterns eventually cause them to blow towards distant shores as they develop, and they often arrive on beaches in the late spring or early summer. The individual Tina and Cindy found may have been a late bloomer. However, the fact that it lacked the sail may mean it just moved much more slowly! These hydroids show polymorphism, or different forms. Some have sails oriented left-to-right and others right-to-left. This causes some to head towards Asia while others sail towards North America. Since winds in the northern and southern hemispheres are reversed, Velella of the same sail orientation drift in different directions in each hemisphere.

I was congratulated by one reader of last week's column because it didn't mention sex... er, reproduction... once. However, without the critical function of mating, life as we know it would not continue... nor would it be as interesting, at least to marine biologists like myself! These hydrozoans reproduce using an alternation of generations similar to many other cnidarians, the phylum with stinging nematocysts they belong to. The reproductive polyps produce thousands of tiny (1/25th inch) jellyfish-like medusae. These medusae drift in the plankton for about three weeks before releasing eggs that ultimately develop into the hydroid you see in the accompanying pictures. There, that's a safe, clinical description of their sex life!

NOTE: As it turned out, the critter I looked at was actually NOT Velella velella but its close relative, the blue button (Porpita porpita). My bad. Therefore the image has been changed to show an actual Velella velella.

© 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!

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Velella velella stranded on beach showing curvature of the "sail."

This document maintained by Dr. Bill Bushing.
Material and images © 2009 Star Thrower Educational Multimedia