As the world’s oceans undergo a dramatic rise in temperature, jellyfish blooms have become a regular occurrence, threatening both beachgoing tourists and coastal infrastructure around the world.
But experts are also scrambling to explain a rise in reporting of jellyfish blooms in one of the last places anyone would expect: the freshwater lakes of middle America.
In the dog days of summer this year, local news outlets began reporting on sightings of rare freshwater jellyfish drifting in all manner of freshwater sources: from the Midwestern waters of Lake Erie to ornamental ponds of northwest Arkansas to the oxbow lakes of Oklahoma.
Technically known as Craspedacusta sowerbii, or “peach blossom jellyfish,” the freshwater critters measure in at about the size of a penny. Sporting translucent bodies with a white-greenish tint, peach blossom jellies have anywhere from 50 to 500 tentacles, four of which can grow to be “very long,” according to a US Geological Survey factsheet.
Unlike their sea-bound brethren, the freshwater jellyfish don’t pose a threat to humans. They do, however, pose a threat to American freshwater ecosystems. Native to the shallow pools which dot the sides of the Yangtze River in China, peach blossom jellyfish were first recorded in the Great Lakes region as early as 1933, assumed to have migrated as a byproduct of the global fish trade.
The USGS describes freshwater jellyfish as opportunistic predators, feasting on small organisms that drift too close, like zooplankton, arthropods, and occasionally, fish larva. With few known predators aside from crayfish, peach blossom jellies threaten native freshwater fish in the competition for resources.
One team of researchers, in a joint research venture between Wheaton College in Illinois and the University of Kansas, set out to trace the proliferation of freshwater jellies into the Midwest, and the threats they pose to local food chains.
“We’ve been trying to figure out the cues that control some aspects of the Craspedacusta life cycle,” Nadine Folino Rorem, one of the study’s authors said in a National Oceanic and Atmospheric Administration blog. “Our objective was to assess where jellyfish fit in food dynamics, and competition dynamics as well.”
Starting in 2022, the nearly three-year effort identified four distinct “lineages,” each of which is able to endure wide temperature fluctuations. While the studies suggests the jellies may depend on seasonal temperature changes to complete their lifecycle — conditions more similar to the Midwest than the subtropical south — the authors also noted that they’re likely to thrive as overall water temperatures rise.
“We found that different populations reacted the same to temperature factors, which means if temperatures increase, you’re probably going to see a similar response in different locations in northern Illinois and Indiana, meaning increases in some of these life cycle stages,” said Rorem. “Since scientists are seeing increases in jellies in marine environments due to increases in water temperature, we’re thinking we’re probably going to see a similar situation with Craspedacusta.”
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