How many of you remember back to your high school biology class? I'm not talking about that blonde cheerleader or the football team captain who sat next to you. I'm talking about learning the major groups biologists have broken the animal world into, the phyla. You know, "spiny skinned" critters like starfish (er, sea stars), sea urchins and sea cucumbers are in the Phylum Echinodermata. Jellyfish (er, sea jellies), corals and sea anemones are in the Phylum Coelenterata... oops, that is now called the Phylum Cnidaria. And vertebrates like fish, birds and humans are in the Phylum Chordata because we have a central nerve chord.
Those of you who are not fans of Darwin (and I'm not referring to Scott and Kathy Patterson's dog), may not be happy to learn that in addition to fish, birds and humans; there is another group that qualifies as a chordate despite the fact it looks like a jellyfish (er, sea jelly) and has no spine. I'm referring to the gelatinous invertebrates known as salps, planktonic members of a larger group known as tunicates which includes nearshore forms that attach to the bottom. If you don't like being related to apes, you're definitely not going to be thrilled to be related to these critters which are largely composed of water! And the link... evidence of a central nerve chord (notochord) during their development.
SCUBA Luv recently took us out to the 277 Bank on a shark dive. Nothing like maintaining buoyancy in water that is about 1,600 feet deep! Just don't drop your camera (I tethered mine securely to my BCD). Mayor Bob Kennedy was captain of the King Neptune that day, just as he admirably captains the "Ship of State," our quaint little city of Avalon. Dive master Tim Mitchell set up a hang bar for the divers (no wimpy old shark cage this time), and soon had a mako shark coming in close. I jumped in the water with my camera in hand. It was a while before any of the customers entered the water... perhaps they were waiting to see if the makos and blues made mincemeat of Tim and me. We were able to get some good footage with close passes by two makos. Ah, but that's a story to be told in a later column.
The waters 12 miles offshore were teaming with macro plankton; large, mostly gelatinous critters that drift with the ocean currents. All around us were "jellies" that looked like jellyfish (er, sea jellies), but weren't. There were ctenophores, also known as comb jellies; siphonophores (relatives of the Portuguese man-of-war and likewise equipped with singing cells); and the subject of today's column, the salps. I'm going to focus on the dominant species we saw, Cyclosalpa affinis. I'm sorry, but there is no common name... despite the fact that there were "billions and billions" of these translucent thingies all around us.
Cyclosalpa affinis is a very interesting critter. Salps are much more complicated than the sea jellies, as one would hope based on its classification in the Chordata along with us! There are two quite different phases in their lives. The solitary stage reproduces asexually, forming chains of new individuals by budding. These new salps are grouped into circular whorls with about a dozen individual zoids in each. These whorls may be linked together to form long chains. The individual phase has a test up to about 4" long. The test is encircled by seven bands of muscles that cause it to contract and propel itself by pushing water out of the test.
The zoids in the whorls produced by the solitary asexual phase, join together. They reproduce sexually, producing the equivalent of sperm and eggs. Salps are protogynous hermaphrodites (anyone remember that term?). This means that the young are initially all female, but later turn into males. Thus the older males fertilize the young females. Hmmmm. The fertilized eggs remain attached to the parent and develop there. Of course this "alternation of generations" makes many salps harder to identify because the two phases may look quite different.
Cyclosalpa affinis is known from temperate and tropical waters throughout the world. Its northern-most range along the West Coast is throughout California with occasional records as far north as the Gulf of Alaska. They are strictly oceanic, living out in open water away from the coast. The species was first described by Chamisso back in 1819. There are only about two dozen different species of salps world-wide.
These salps feed on plankton, filtering it out of the water column often at very high rates using a cone-shaped mucous net. In fact, the larger the salp, the faster it pumps and filters water for food. It has been said that this species can munch half its body weight in a day, a feat equivalent to me eating 120 pounds of prime rib a day. Burp! They are said to be among the fastest growing multicellular animals on the planet. When plankton levels bloom, these salps can quickly reproduce asexually to expand their population many fold, and take advantage of the increased food supply. Their population growth rates may be 10 to 100 times that of other animal plankton.
But, you are what you eat, minus what you excrete! Salps may take in prodigious amounts of food, but this means they also produce prodigious amounts of fecal matter. The constant "rain" of this fecal matter falling towards the ocean floor creates a food resource for many mid- and deep-water organisms. It is one mechanism whereby organic matter is transferred from the highly productive near-surface waters to the deep ocean. Whale poop is another such mechanism.
Salps are fed on by other "jellies" like ctenophores and siphonophores, and by more advanced predators like sea turtles, marine birds and many different species of fish. They have more edible tissue than a similarly sized sea jelly or ctenophore, which are mostly water, and therefore provide a more concentrated food source. Salps may also provide homes for hitchhiking copepods, amphipods and even small fish. Of course those critters have to be very careful... since they live in what is the equivalent of a glass... er, gelatinous... house.
NOTE: There is an excellent video about diving Catalina Island that is available over the Internet on the Bloomberg Financial News' website. It features interviews with Jean-Michel Cousteau, Mayor and SCUBA Luv co-owner Bob Kennedy, and Dr.Bill. The video was put together by Matt and Nadja Brandt for Bloomberg. To see it, log onto the Bloomberg web site (www.bloomberg.com), and search the site on the keywords "Cousteau" and "giant sea bass." You can read the accompanying article by Nadja, then to the right of it select the accompanying media "Diving in the Emerald Forest off Catalina." It's a pretty nice introduction to our underwater world and why many of us love to dive here.
© 2007 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. Please help me climb out of self-imposed poverty... buy my "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles," "Gentle Giants: Giant Sea Bass" or "Common Fish and Invertebrates of the Sea of Cortez" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!
Divemaster Tim Mitchell filming salp chain, enhanced images of Cyclosalpa affinis chain, and solitary asexual phase of this salp species
This document maintained by
Dr. Bill Bushing.
Material and images © 2007 Star Thrower Educational Multimedia