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Dive Dry with Dr. Bill

#601: By-the-Wid Sailor Home From the Sea

Several years ago, I wrote a column about a marine critter that Tina Quinn and Cindy Rinehart brought up to my house for identification. In that column I stated it was a by-the-wind-sailor, known scientifically as Velella velella. Today I have to apologize to them and to my readers for a case of mistaken identity. I learned later that the critter they showed me was Velella's cousin, Porpita porpita (or "the blue button" in non-scientific language). Within the last three weeks we have had influxes of both species on our shores so I thought I'd better correct my mistake through this public forum.

I will admit that I need to get my eyes examined (and some think my mind as well) but this mistake should never have been made. Although the two species are closely related, even a child should be able to tell them apart with the proper information. Of course I'm still a child at heart, but no more excuses! Both species have "disks" that look like they are made of plastic and a fringe of beautiful blue tentacles on the disc's edge. However, Porpita is circular in shape while Velella is oval, and it also lacks the vertical "sail" found on its cousin. Thanks to Renzo and Al of the SCICo boat crew, I was able to come down and photograph the specimens presented with this column.

Both species are drifting "floaters" using small amounts of gas trapped in their disks. My readers are undoubtedly familiar with plankton that drift with the ocean currents, often submerged at significant depths. Because they float right at the ocean's surface, Velella and Porpita are consider neuston and are part of an interesting ecological community that resides in the very top layers of our Ocean Planet. Obviously they are non-divers!

When I first encountered Velella many decades ago as a kid on the northeast coast of Florida, I was too young to read the scientific literature (or even Dick and Jane books). Perhaps that was a good thing since there has been some dispute about them among taxonomists, those biologists who classify critters into our human-defined categories. Even when I arrived on Catalina in the late 1960s many taxonomists thought these drifters were siphonophores related to the Portuguese man-of-war or our local species in the genera Apolemia and Praya, or the hula skirt siphonophore (all of which I've written about previously). I've been stung by the first two, but neither holds a candle to the man-of-war. Mom found that out one day on the Florida beaches as little Dr. Billy was out catching sand crabs!

Although they are distant relatives of those stingers (as well as jellyfish and coral), these two species are considered now to be colonial hydroids. They do possess the stinging cells known as nematocysts common to all their relatives in the phylum Cnidaria. However those on Velella are either not capable of penetrating human skin or their toxins do not affect us... unless you are "unwise" (aka stupid) enough to place your tongue on them! I'm sure none of my readers would do that... right?

Scientists still debate whether Velella is a complex colony of specialized individuals or a single organism. Whichever turns out to be true, some polyps (tentacles) are adapted to feed ("munching"), others for reproduction ("mating") and a third type with stinging cells for defense. The individual components may be specialized but each polyp is connected to a common digestive gut so they all share any food captured by the feeding polyps. These hydroids are carnivores feeding on small prey including fish and crustaceans just below the water's surface. Yes, I know... it is hard to view them in the same light as a lion or a shark, but think of it from their prey's perspective. Just as deadly! 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 snails known as nudibranchs including 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. 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.

Of course I would be totally remiss if I didn't mention mating as well as munching. As I often say, munching allows the individual to survive and grow but the ultimate purpose is mating so the species itself continues. Without the critical function of mating, life as we know it would not continue... nor would it be as interesting, at least to lecherous marine biologists like myself! These hydrozoans reproduce using an alternation of generations similar to many other cnidarians.. 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! Are you happy, or did you expect all the gory details?

© 2014 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). 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 from the side and from above; two floating in a bucket and their cousin Porpita.

This document maintained by Dr. Bill Bushing.
Material and images © 2014 Star Thrower Educational Multimedia