Jellyfish in Idaho? Rare sighting made in freshwater pond in Star

While swimming in the east pond at Freedom Park in Star, Marc Brandes saw something peculiar in the water in front of him.

“I thought it was a feather, or some gross mucusy thing floating around there,” Brandes said. “Then I realized it was moving.”

He had his daughter grab a bucket, and together they scooped up a tiny translucent-white jellyfish.

Moments later, the Brandeses started noticing more, and catching the coin-sized creatures became a game.

“My other two girls got involved, and by the time we were done they had caught about 15 or 16 of them in a bucket, and they were just kind of like, ‘Oh my gosh, this is crazy,’” Brandes said told the Statesman. “I never knew there was such a thing as a freshwater jellyfish.”

While rare, freshwater jellyfish have been spotted in Idaho for at least the last 30 years. The non-native species can lay dormant for years at a time without reaching full maturity. Nobody knows for sure how they move from one body of water to the next, but they’ve been found in 45 states in the last century and on every continent except for Antarctica.

Scientists are unsure about what this means for freshwater ecosystems, but the relationship between jellyfish and ocean ecology is well documented. Research into saltwater jellyfish has found that as ocean temperatures rise, so does the frequency of jellyfish blooms. These sudden explosions in jellyfish populations are increasingly triggered by overfishing their natural predators, and when millions of jellyfish suddenly emerge, they consume massive amounts of plankton and fish larvae, disrupting food chains and fish hatcheries. Recent blooms have also caused beach closures at various sites around the coastal United States.

After encountering them in Star, Brandes reached out to Idaho Fish and Game and the Idaho Department for Environmental Quality to see if he should be concerned. Other than knowing that the jellyfish are harmless to humans (their stingers can’t penetrate human skin) and that they’ve been in Idaho a long time, they didn’t have much information for him.

“Obviously we don’t like seeing introduced species because there’s always a risk that they’re going to be harmful or they’re going to bring some disease that we don’t know about,” Joe Kozfkay, the state fisheries manager for Idaho Fish and Game told the Idaho Statesman. “But freshwater jellyfish have been around for a very long time. They don’t seem to be increasing in abundance, nor have we noted any sort of deleterious effects on native species from them.”

A ‘little mystery’ waiting to be solved

The freshwater jellyfish, or craspedacusta sowerbii, isn’t a fish at all but belongs to a phylum of invertebrates called cnidarians that are almost entirely made of water. Sometimes called the “Peach Blossom Jellyfish,” it is native to the Yangtze River in China, these freshwater jellies most likely made their way to new habitats around the world as larvae, hitching rides on the exotic water plants and fish taken out of China and sold in pet stores around the globe, researchers said.

In their adult phase, these little buggers eat whatever their up to 500 tentacles can grab onto, which as it turns out, isn’t much. They eat only certain sizes of tiny organisms like plankton, and while four scientists the Statesman spoke to say jellyfish could affect native species, very little is known about how freshwater jellyfish move from one body of water to the next.

“It’s really hard to study them because they show up suddenly, and they don’t show up every year,” said Frank Wilhelm, a professor of limnology at the University of Idaho who studies the inland aquatic ecosystems. “It might be 10 years between their emergence as adults in their life cycle, and then they’re around for a week to 10 days.”

Freshwater jellyfish spend most of their life cycle as polyps. When a jellyfish is in its larval stage, called a planula, it swims through the water until it bumps into an aquatic plant or rock, where it can attach itself to the surface and remain there for years or decades as a polyp. These polyps can divide to produce more polyps, but conditions need to be just right for them to morph into adult jellyfish, called medusas.

Unlike saltwater jellyfish, they have a ring of muscular tissue called a velum under their bell-shaped bodies that allow them to swim more efficiently.

When looking for freshwater jellyfish in Idaho, you need a lot of luck. They need water that’s at least 25 degrees Celsius, or 77 degrees Fahrenheit, to trigger those polyps to transform into mature adults. Because they don’t make this transition annually, Wilhelm said, scientists still don’t know what exactly the jellyfish need to reach their final form and reproduce sexually.

“For now, it’s still a little mystery for some eager scientist to solve,” Wilhelm said.

While on his way to a rafting trip on the Lower Salmon River in 2013, Wilhelm learned about a secret pool in an offshoot of the river from a stranger pumping gas across from him on his way to the launch site.

“He said there was this amazing thing happening about halfway down the river route, but you had to steer your raft over to a connection to this hidden pool, and if you weren’t in the right position when you approached, you’d get pulled into the rapids and miss it,” Wilhelm said.

When Wilhelm found the pool, he could hardly believe his eyes.

“It was like seeing snow falling under water — thousands of jellyfish in this little pond,” he said. “I just felt like I’d stumbled into some other world. If it wasn’t for a stranger at a gas station telling me about this, I would’ve never known they were there.”