News from the SLA: This is not a fish story
BY Robert Werner, Ph.D.
Recently, we received a note from Laurie LeFever regarding an odd creature that her son Jacob had taken from the lake near Fallbrook Point. Jacob was canoeing in a quiet bay on the north side of the point when he noticed a semi-transparent blob swimming in the water. He quickly paddled to shore got a small bucket and hurried back and captured it. Once he was back on shore he and his mother took pictures which showed a small jellyfish about the size of a walnut with a nearly transparent bell and relatively short tentacles. A jellyfish you might say! Who ever heard of a jellyfish in freshwater? Well, there is one. Its name is Craspedacusta sowerbyi or simply freshwater jellyfish.
Freshwater jellyfish are native to China, but have now spread to all continents except Antarctica. It is widely found in the U.S. How it got here is a bit of a mystery. The most likely avenue is that they were transported on ornamental aquatic plants or with live fish meant for ponds. In China, they occupy shallow water ponds.
It has a rather unusual life history alternating between two totally different life forms: the polyp and medusa stages. The medusa reproduces sexually by expelling gametes into the water where fertilization takes place. The eggs hatch into planula larvae which swim for a short time before settling on the bottom and developing into the polyp stage. The polyp attaches to the bottom by its trunk like midsection and with tentacles extending out into the water feeds on small zooplankton. The medusa stage forms from buds produced by the polyp and it is the free-swimming jellyfish stage. It captures food by swimming up toward the surface and then drifting downward with its tentacles extended. When the tentacles encounter its zooplankton prey nematocysts on its tentacles sting the zooplankton, immobilizing it so that it can be consumed.
The polyp stage is very inconspicuous on the bottom and is difficult to locate. The medusae are more conspicuous and appear sporadically, sometimes in large numbers, but quickly disappear for years and then reappear. Little is known as to why this happens.
This is an exotic species, but not one that is likely to cause much trouble. It is too small to be a danger to humans. Its nematocysts are unable to penetrate human skin. The most likely impact would be to reduce or modify the composition of the zooplankton population of the lake. In the small numbers at which it is found and the infrequent occurrences of it one would not expect any significant impact at all on Skaneateles Lake zooplankton.
So, keep your eyes peeled for a nearly transparent jellyfish swimming near the surface. Chances of seeing one are best on a calm day in a shallow sheltered location. Enjoy this interesting, harmless part of the always fascinating Skaneateles Lake ecosystem.
With thanks to the SLA Invasive Species Monitoring Steward who encouraged Laurie to share this “find” with the SLA.
Pictures can be viewed on skaneateleslake.org.
Please thank the following individuals whose generous donations, in addition to their annual membership fees, supported the Milfoil Boats for a day or multiple days. We simply could not have done what we are doing this year and plan to do next year without them.
Vincent Dopulos and Christine Larsen, The Kaufman Foundation, The Dwight W. Winkelman Foundation, Edward and Deborah Brennan, Joe and Mary Ellen Hennigan, Gianfranco and Johanna Frittelli, Peter and Elsa Soderberg, Paul and Kathy Leone, Dave Birchenough and Carrie Lazarus, Ted and Nancy Norman, Bill and Donna Davis, Steve and Jackie Miron, Bill and Janet Allyn, John and Lousia Cohlan, David Duggan and Lynn Cleary, Christopher and Amy Neumann, Arnie and Libby Rubenstein, Peter and Jane Hueber, John and Candace Marsellus, Kenneth and Marjorie Blanchard, Sidney and Suzanne Devorsetz, John and Elizabeth McKinnell, James and Julie Moore, Ed and Maggie Dienst, Jerald Gebo and Bill Rosenthal, The Slottje Family, James and Kimball Kraus, John Macallister and Laurel Moranz, James and Salli Tuozzolo, Joseph and Katherine Compagni, David and Sherill Ketchum, Doug Wood and Barbara Conner, Lindsay Groves, Greenfield Lane Association, Roland and Tacie Anderson, Jeffrey Kirshner and Lorraine Rapp, Eric Yopes and Amelia Kaymen, Anonymous 3, Robert and Sara Neuman, John Osborn, James Pulaski, Curt and Susan Andersson, Lois Exner, The Rothenberg Family Foundation, Lew and Dawn Allyn.
Join the SLA at SkaneatelesLake.org or call 315-685-9106 and request that an Annual Member Registration Form be mailed to you.