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Jellyfish Emerge in Twin State Ponds

Valley News Staff Writer
Published: 10/12/2018 11:58:01 PM
Modified: 10/15/2018 4:03:37 PM

Lyme — About an hour before a spectacular sunset lit up the surface of Post Pond, Matt Stevens peered over the side of the canoe gliding along the shoreline, and then turned to his friend, paddle in hand.

“Those are jellyfish,” Stevens said.

“Shut up,” came the reply.

Stevens, a conservation resource manager with the Appalachian Trail Conservancy, has heard that same tone of disbelief from pretty much everyone that he’s mentioned the jellyfish to — it’s as if he said he’d seen a shark, or a deep-sea squid trolling among the loons and lily pads.

But in fact, freshwater jellyfish have been observed in New England for at least 50 years, and 2018’s unusually hot summer has led to ideal conditions for dozens, or hundreds, of the elusive aquatic creatures to appear in the water.

This was the second-warmest September on record, according to the Vermont Department of Forests, Parks and Recreation, and climate change is likely to lead to more long, hot summers in the future. Experts say those warmer waters ultimately will change the ecology of places like Post Pond, which earlier this summer was the subject of a cyanobacteria advisory by the New Hampshire Department of Environmental Services after the heat-loving, toxic bacteria was found on Chase Beach.

Jellyfish blooms are far less worrisome than algal blooms, according to Jim Kellogg, an aquatic biologist with the Vermont Department of Environmental Conservation who has been keeping track of the quarter-sized jellyfish for years.

They do sting their prey, but they’re too small for a human to even notice. And while the jellyfish kill tiny fish and zooplankton, any harm they do to fish populations seems to be counterbalanced by the fact that larger fish can snack on the jellyfish, Kellogg said. Kellogg said there is disagreement in the academic literature over whether the jellyfish are native to the region, or whether they are actually an invasive animal from China.

In fact, there’s a lot of mystery to New England’s jellyfish.

For nearly 20 years, Kellogg has recorded each reported sighting into a database of Vermont lakes and ponds that he curates for that purpose.

“I have a list of 11 lakes,” Kellogg said, none of which are in the Upper Valley. The sparseness of observations is in keeping with the jellyfish’s natural elusiveness.

“You may see two, or you may see 102. They’ll be there one minute, and an hour later, they’re gone. You may see them one year and not the next,” he said.

Kellogg said the only Vermont site that has anything like regular sightings of the ephemeral jellyfish — Craspedacusta sowerbyi to biologists — is Greenwood Lake in Woodbury. Like many animals, they typically hop from one lake to another on the feet of aquatic birds, or the hulls of boats.

Though they rarely are observed in a body of water for two consecutive years, they often are present as nearly invisible cysts or polyps, clinging to the surface of a rock or log and eating tiny microorganisms. Only when conditions are right do they develop into medusa, the bell-shaped, bulbous form that is reminiscent of their saltwater cousins.

“You can sort of see that they’re semi-translucent,” said Stevens, who had a second sighting of the jellyfish in Indian Pond in Piermont on Sunday. “They’re like a bit of brightness in the dark water.” With more than 50 observation sites, New Hampshire has had many more jellyfish-infested ponds than Vermont, though Kellogg said this is likely the result of a more robust and active reporting system.

He said people seeking a rare jellyfish encounter should try still waters on rainless days, when the water is near its peak temperature, typically from late July through October.

Those who see jellyfish in New Hampshire are encouraged to email or call 603-271-0698, while those who see them in Vermont are asked to contact Kellogg at or 802-490-6146.

Matt Hongoltz-Hetling can be reached at or 603-727-3211.

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