The idea of jellyfish inhabiting a vast freshwater lake like Erie might seem surprising. Marine jellyfish cannot survive in Lake Erie. However, a distinct freshwater organism, often mistaken for a jellyfish, leads to occasional sightings.
Why Marine Jellyfish Don’t Live in Lake Erie
Marine jellyfish cannot survive in freshwater environments like Lake Erie due to fundamental biological differences concerning salinity. These organisms are osmoconformers, meaning their internal salt concentration largely matches their surrounding ocean environment. Ocean water contains a high concentration of dissolved salts, reflected in their internal chemistry.
Freshwater, by contrast, has a significantly lower salt content. If a marine jellyfish were introduced to Lake Erie, the drastic salinity difference would cause water to rapidly move into its cells through osmosis. This influx would lead to the cells swelling and eventually bursting. The osmotic challenge posed by freshwater is a direct barrier to marine jellyfish colonizing inland lakes.
Introducing Freshwater Jellyfish
The freshwater organism, scientifically known as Craspedacusta sowerbii, is often referred to as the freshwater jellyfish. This hydrozoan species is distinct from the larger scyphozoan jellyfish found in oceans. Adult medusae of C. sowerbii are small, typically measuring between 5 and 25 millimeters (0.2 to 1 inch) in diameter. They are translucent with a whitish or greenish tint, possessing a bell-shaped body with 50 to 500 tentacles used for feeding.
The life cycle of C. sowerbii involves both a polyp stage and a medusa stage. The polyps are tiny, sessile organisms that attach to surfaces and reproduce asexually by budding, forming colonies. Under certain environmental conditions, these polyps produce free-swimming medusae. This species is native to the Yangtze River valley in China but has spread globally, inhabiting still or slow-moving freshwater bodies like ponds, quarries, and reservoirs.
Are Freshwater Jellyfish Found in Lake Erie?
Craspedacusta sowerbii can occasionally be found in Lake Erie, though their presence is rare and sporadic. Sightings typically occur in calm, warm waters, often near the shore or in sheltered embayments. Recent observations include areas like Presque Isle Bay in Pennsylvania and near Put-in-Bay, Ohio.
This species is non-native to North America, introduced from China as early as the 1880s, possibly via ornamental aquatic plants, stocked fish, or waterfowl. These freshwater jellyfish are not dangerous to humans. Their tiny stinging cells (nematocysts) paralyze small prey like zooplankton and are too small and weak to penetrate human skin. Their impact on the Lake Erie ecosystem is not well understood. Other small, translucent organisms, such as certain insect larvae or zooplankton, might also be mistaken for jellyfish by casual observers.