Craspedacusta’s last fight? Unlikely, but now is the best time to see the Crim Jellies

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  • Soaking for jellies:

    Martha Young ’24 collects a water sample from Crim Dell Pond, which is currently experiencing a massive bloom of adult freshwater jellyfish. Biologist Jon Allen has enlisted Young and other members of his BIOL 302 class in an investigation of this mysterious species.
    Photo by Jon Allen

by Joseph McClain

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September 16, 2021

Crim Dell jellyfish are back, bigger and more numerous than ever.

Jon Allen says the Craspedacusta jellyfish are blooming in Crim Dell Pond. Freshwater jellyfish usually hide invisible, deep in the depths of the pond in their planula and polyp stages. But every few years, the adult forms, known as jellyfish, make their presence known on campus as they swarm to the surface in a sprawling – and presumably unsuccessful – search for mates.

“My guess is that there are at least thousands – tens of thousands?” hundreds of thousands? – from jellyfish to Crim Dell, ”Allen said. “Hopefully we can get a better tally this fall to figure out how much.”

Allen, associate professor in the biology department at William & Mary, said the last bloom observed was in 2019. Jellyfish flowers are mysterious and difficult to predict, he added.

“When I first got to William & Mary, I was told they bloomed every eight years or so,” Allen said. “This pattern lasted for one cycle, with one flowering in 2010, then another in 2019 – a period of nine years. But now we are only two years since the last flowering observed and this one is much more important than the two previous ones. “

Happily, this year’s bloom coincides with Maria Clagett and Martha Young’s enrollment in BIOL 302 – Integrative Biology: Animals, Taught by Allen.

“They both told me they were interested in jellyfish when we first met and I’m sure I disappointed them saying that we mainly study other types of thornless creatures,” he said. -he declares. “The return of the Crim Jells coinciding with the students interested in jellyfish was just luck! “

Clagett and fellow BIOL 302 student Mariel Webb, both members of the 2024 class, were the first to see the Crim Jells. Allen said they spotted the jellyfish from the Crim Dell Bridge. During normal bloom, jellyfish are too small – at best a penny size – to be easily seen without having one in your collection net. But this year’s jumbos are about the size of a quarter, large, and numerous enough for occasional naked-eye jellyfish fishing.

“They are probably easier to spot from the sidewalk between ISC and Sadler,” Allen said. “If you walk past when the light is dimmer in the morning or afternoon, they’re pretty easy to see.”

We know very little about Craspedacusta astonished. Allen explained that it is an invasive species, native to China. They are found in other ponds, not just Crim Dell. But beyond a few simple facts, Allen says more questions than answers surround the jellyfish. Webb and Clagett have joined Allen’s lab to use the big bloom of 2021 to try and answer at least some of the questions.

A strange set of facts centers around the arcane of Craspedacusta the reproduction. Allen explained that small polyps reproduce asexually, cloning themselves to introduce new generations of Crim Jells. The business of jellyfish, however, is to mate and reproduce. But the members of a Craspedacusta bloom are almost always one sex or another. It’s the same this year.

“So far they are just females – with lots of eggs!” Allen said. “But no men. Is there sexual reproduction in Crim Dell or not? Not clear!”

He said the jelly lab would try to get the Craspedacusta spawn in vitro, and also study whether these egg-laden females will reproduce parthenogenically. It’s not just the exotic breeding habits of jellyfish that are unknown; Allen says there’s a lot to pin down in the nuts and bolts lane of the freshwater jellyfish life cycle.

“We don’t even know what caused this bloom,” he said. “Probably a combination of warm temperatures and plenty of food for the jellies, but we don’t really have a good idea of ​​their diet.”

Allen said the group started collaborating with “Flatworm Mom and now Jellyfish Guru” Anna Klompen ’11, an Allen Lab alumnus. Klompen is now in graduate school at the University of Kansas.

“Hopefully we can get to a point where she can use some of the Crim Jells in her graduate work,” Allen said. “She now has some of the same species in Kansas, but they are from Japan. Apparently, North American populations are not available. Hope we can change that!


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