Freshwater Jellyfish – News and Stories

S

impl and complex are antonyms, but not with jellyfish.

Jellyfish lack brains, bones, hearts, and lungs. Over 95% of their body is made up of water. Early scientists wondered if jellyfish were even animals, generally calling them “zoophytes”, intermediaries between animals and plants.

Jellyfish meet modern biology criteria for classification as animals, but despite their name are not fish. Their lack of a backbone makes them members of the phylum Cnidarian, which includes corals and sea anemones.

Freshwater jellyfish (Craspedacusta sowerbyi) are found throughout the United States and on every continent except Antarctica. They have even been found in bodies of water in Indiana, including lakes, ponds, streams, and rivers.

“They are unpredictable and episodic,” explained Reuben Goforth, associate professor of aquatic ecosystems at Purdue College of Agriculture. “Jellyfish can suddenly appear in a lake where they have never been recorded and may not be seen for years.”

Goforth explains that sightings generally occur in August and September during the hottest weeks of the year.

“Freshwater jellyfish exist in a resting phase for long periods of time. Sometimes they transform into a mobile jellyfish stage coinciding with the availability of their prey, zooplankton.

When freshwater jellyfish encounter zooplankton, stinging cells in their tentacles called cnidocytes are triggered. Jellyfish fire small projectiles that release a toxin to immobilize their targets. Then the tentacles drag the paralyzed prey into the jellyfish’s body where they are slowly digested.

Fortunately, predators pose no threat to humans. While saltwater jellyfish are known to sting swimmers, their freshwater counterparts rarely grow to an inch in diameter, remaining too small to break human skin with their tentacles.

The non-native species is believed to be native to the Yangtze River in China. While it is not known how they got to America, scientists have a better understanding of how they travel across the state, Goforth explained.

“There seems to be a fair amount of evidence to suggest that they are spread by waterfowl. They can stick to the legs and feathers of birds when traveling.

Goforth warned that any time new species are introduced to an ecosystem, its balance could be threatened. However, according to his observations, the impact of freshwater jellyfish in Indiana was more of a ripple than a wave.