Freshwater jellyfish have been hanging out in inland lakes and rivers throughout the Great Lakes region since 1933. But a century after their discovery, we still don’t know much about the elusive creatures.
Craspedacusta sowerbii is a native of the Yangtze River in China, but the tiny creatures (fully grown, about an inch in diameter) can now be found in slow-moving waters in Europe, North America, and other places around the world.
Its life cycle includes polyps living in colonies, feeding and budding and occasionally producing sexually reproducing medusas. Medusas’ fertilized eggs settle to the bottom and develop into polyps. Most populations in the U.S. are either all male or all female, producing no sexual reproduction.
Similar to its larger cousins, Craspedacusta medusas are surrounded by many tentacles, which capture prey and pass it on to the mouth. Diet consists of fish eggs and larvae, zooplankton, water mites and insects, which its mild sting is sufficient to immobilize. The scientific community is not greatly concerned about this exotic species, but populations occasionally spike in warm weather (water temperatures above 77 degrees F), suggesting that it can reduce zooplankton populations significantly. Scientists would like to know more about this secretive creature. A team of student scientists in Michigan is on the case.