Freshwater jellyfish. Video: Debra Marnich

Jellyfish in Chocorua Lake

by Juno Lamb

Invasive, but also sporadic and unpredictable, elusive, even ephemeral—all these terms are applied to the freshwater jellyfish. What can we learn from the surprising and magical appearance of these tiny, elegant creatures in Chocorua Lake in 2022?

Local swimmer Bob Schor got in touch with us this past September. He’d swum in Chocorua once, a few years ago, and then been reintroduced to the lake in August by Chocorua Lake Basin resident Kristina Folcik, who proposed a group swim to members of the Mount Washington Valley Running Club. She gave him, he says, “a great re-introduction to the lake that made me want to swim there more often.”

Freshwater jellyfish. Click on any of the photos to view larger. *Photo: Debra Marnich*

So he did, and noticed nothing unusual—until September 9. That day, he and his friend “swam north toward Mount Chocorua” from the Grove. “Maybe 50 feet out or so, I began to notice, looking down through my goggles, what looked like translucent or pale white flower petals floating below the surface. I thought it was odd, thinking they might be some sort of seed pods, and continued my swim. It wasn't until later, when we were coming back towards the Grove, that I began to notice them again and since we were pretty much done with our exercise, I looked closer and couldn't believe that they were actually jellyfish! I excitedly called to my friend, ‘Come here. Jellyfish!’ and she either thought she heard me incorrectly or that I was crazy. But, sure enough, she came over, looked, and couldn't believe it either. We both became mesmerized watching them swim and shared the news with another swimmer, who also was amazed.”

Freshwater jellyfish (Craspedacusta sowerbii), also called peach blossom jellyfish—perhaps because, as Bob noticed, they look like flower petals beneath the surface of the water—are roughly the size of a penny in their “adult” medusa form, and they look like…drum roll…jellyfish! Translucent, with a whorl of 50 to 500 tentacles around the bell margin, they move through the water with the same pulsing motion we imagine when we think of saltwater jellyfish. And while they also sting like the jellyfish that they are, they are so small that only tiny invertebrates need worry.

Originating in the Yangtze basin in China, C. sowerbii are now found in freshwater on every continent except Antarctica. They appear in places they’ve never been spotted before, as they did in Chocorua this past summer, and, according to New Hampshire Department of Environmental Services (NHDES), “they may appear again in a few years, or not at all!” (Freshwater jellyfish have been sighted in 63 NH water bodies to date—not including Chocorua! Tamworth resident Dylan Alden recalls seeing them at Bearcamp Pond in late August of 2018 or 2019.)

Freshwater jellyfish. *Photo: Debra Marnich*

Part of why they’re rarely spotted is that they are only visible to human eyes in their medusa phase, which, according to Michele Condon from the Water Division of NHDES, “occurs for typically only a short period of time when the conditions are ideal (warmer water). During the medusa phase, the freshwater jellyfish are free-swimming and will often appear near the surface, forming what’s often described as a ‘bloom.’” These jellyfish spend much of their life cycle as a tiny polyp, attached to a surface or hiding in muck at the bottom of a pond, and are able to reproduce both asexually by budding off ephyras (immature medusas) as well as sexually in their medusa stage, which results in a zygote that becomes a planula (larva) and then a polyp!

Their miniscule size in immature phases makes it easy for them to hitch a ride from one place to another. As Michele Condon points out, “There have been sightings in New Hampshire lakes for many years, but each year there are new water bodies. The freshwater jellyfish (most often in polyp form) may be transported to a new waterbody by other plants, fish, waterfowl, or boats.” Another cause for their intermittent appearances and disappearances, according to a team of scientists published in Scientific Reports, is that, “Under unfavorable environmental conditions (e.g., low temperatures and food concentration), formation of resistant polyps (e.g., podocysts) has been observed, which can survive up to forty years of desiccation.” In other words, these podocysts can be inactive, but still alive, for four decades!

Why might something so intermittent and elusive be called “invasive”? The word is often used to describe non-native flora and fauna that outcompete or harm native species and risk disrupting the ecological balance that has evolved in a particular location. These species may have been transported by humans for decorative or practical use (or by mistake), without a full understanding of what native species they might impact; they might have hitched rides on birds or mammals; they may be moving to new locations in response to a changing climate or because land has been disturbed. In the case of the jellyfish, the designation comes from the concern that as the climate warms in response to human activity, the jellyfish may become more abundant. This in turn might disrupt aquatic food webs as the jellyfish consume zooplankton that are currently food for other native aquatic species. We don’t lack reasons to work to slow the ship of climate change, and in the meantime, these ephemeral creatures are hard for scientists to study because they tend not to stick around in one place!

After his magical discovery, Bob researched the jellyfish online, which led him to contact NHDES so that they could update their list of jellyfish sightings, and got in touch with Chocorua Lake Conservancy, as well. He came back to swim on September 13 and arranged to meet CLC Stewardship Director Debra Marnich to try to collect a jellyfish in a plastic bag for her to see. They were gone! Or they appeared to be…they were no longer in the areas offshore from the Grove. Deb went back to the CLC office, and Bob continued his swim. After a while, Bob said, “I began to notice them again. I caught one in the bag and stashed it on the closest shore and continued my swim. I ended up swimming through many, many intermittent "’blooms’ of jellyfish as I headed across the lake and back, picking up the specimen on my return. I brought the jellyfish to Deb and we put it in her dog's bowl and got pictures and an awesome video. The jellyfish are so cool to watch!” Afterward, Bob returned the jellyfish to the lake, safe and sound.

“While I now know that these are common enough throughout the states,” Bob said, “it doesn't take away from the fun I had in ‘discovering’ something new to me, at least.”

Deb Marnich agreed. “It was such an amazing and interesting experience to see a freshwater jellyfish in a New Hampshire lake in Carroll County after 20+ years of swimming, kayaking, canoeing, and fishing here and never seeing one.”

Part of the magic of an ongoing relationship with a place, including a beautiful place like Chocorua Lake, is that it invites us to notice, learn, and reflect on how the small is connected to the large, and vice versa. And sometimes the small is a tiny translucent jellyfish!

Banner image: Freshwater jellyfish. Photo: Debra Marnich