Fresh Water Jellyfish

Craspedacusta sowerbii  - Wikipedia CC

An article in the News-Leader by Francis Skalecky introduced me to fresh water jellyfish.  Craspedacusta sowerbii is an Asian species of jellyfish accidentally introduced into North America.  According to Freshwaterjellyfish.org - (yes they do have their dedicated website) they are now found in 44 of the lower 48 states.

C. sowerbii jellyfish are small, reaching the diameter of a quarter. They have typical jellyfish features, an umbrella with stringy tentacles attached to the edges. These contain cnidocytes, specialized stinging cells which they use to paralyze their prey, macroinvertebrates and small fish.

They are easy to miss as they are somewhat translucent. Their gonads on the underside may be the first thing spotted before making out their overall shape.  Their lifecycle is difficult for me to grasp, involving podocysts, polyps and frequent asexual reproduction explained below.

"A tiny, stalked form of the jellyfish (the polyp) lives as colonies attached to stable underwater surfaces such as rooted plants, rocks, or tree stumps. The microscopic polyp colonies feed and reproduce during the spring and summer months. The polyps reproduce asexually. Some of their offspring are the jellyfish that can be seen at the surface. The "jellyfish" or medusa reproduce sexually. Fertilized eggs develop into planula larvae which eventually settle to the bottom of the pond or lake and develop into polyps. However, in the United States, most populations of jellyfish are either all male or all female, so sexual reproduction may be rare."  Freshwaterjellyfish.org

The polyps contract in winter forming podocysts or resting bodies which may explain how they have spread to isolated ponds and water bodies, possibly transported by aquatic animals and birds.*   They may be suddenly found in large numbers one year with none the following years.  In some cases they have totally disappeared from a lake.

Although they have stinging cells, there are mixed reports on whether they can sting us.  Many people report handling them with no discomfort while others report mild itching and red spots or a slight numbness. Either way, they appear to be nothing to worry about while swimming in Missouri waters.

* Freshwaterjellyfish has a very detailed FAQ including caring for them in an aquarium.  Although not specifically mentioned, this must be a possible way of spreading them by compassionate dumping of aquarium contents.