Newsletter 8

An Oddity in Connecticut Lakes, the Freshwater Jellyfish (Craspedacusta sowerbii)

Living on the Connecticut shore, I am used to thinking about and encountering jellyfish in Long Island Sound. However, in my travels to various lakes around the state, I occasionally get to see freshwater jellyfish swimming throughout the water column. The lakes where I have seen the jellyfish the most are located in southwestern Connecticut. I normally see them in August to late September. When they appear, they are usually present only for a short time ( few days - week) and then disappear again. I may not see them again for a couple of years in any particular lake.
Because I thought the presence of these jellyfish was interesting, I wanted to do some research and find out more about them. The freshwater jellyfish is believed to originate from the Yangtze River region of China and was introduced into other countries via aquatic plants. It turns out that freshwater jellyfish are more common than I first thought. Freshwater jellyfish have been seen in 45 of the 50 states. The only states not to have a recorded sighting are Hawii, Montana, North Dakota, South Dakota, and Wyoming. The first recorded appearance of freshwater jellyfish in the US occurred in 1908. The species seems to be introduced into new lakes via aquatic plants, fish stockings, and bird activity. In Connecticut, there are at least 40 lakes and ponds that have recorded the presence of jellyfish. A list of lakes / ponds where these jellyfish have been sighted in Connecticut can be found at www.jellyfish.iup.edu.
The majority of the animal’s lifecycle is spent as a tiny polyp attached to sediments, rocks, aquatic vegetation, and other substrates on the lake bottom which is why they are not seen very often. They reproduce by creating buds that form into more polyps that rest on the bottom substrates. When the right environmental conditions are present, these buds form into a medusa instead of another polyp. The polyps produce the medusa in order to reproduce sexually. However, it appears that lakes in the US have either all male or all female jellyfish but not both, making sexual reproduction impossible. The medusa is about the size of a quarter - half dollar, and can be seen swimming in the water column as it looks for tiny invertebrates to eat. The jellyfish are present in this stage for a few months and then disappear and the medusa stage may not reappear for several years.
So next the time you are out on a Connecticut lake in the late summer, keep an eye out for this interesting creature. Don’t worry, unlike the marine jellyfish, these jellyfish do not appear to sting humans.

Chris Mayne, CLM

More information and pictures about freshwater jellyfish can be found at the follwing websites:
http://www.jellyfish.iup.edu.
http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1068
http://en.wikipedia.org/wiki/Craspedacusta_sowerbyi
http://www.des.state.nh.us/factsheets/bb/bb-51.htm
http://animaldiversity.ummz.umich.edu/site/accounts/information/Craspedacusta_sowerbyi.html