The Unsolved Mysteries of the Crim Dell Jellyfish

The thousands of jellyfish in the Crim Dell have come and gone and come back again. But why and how? Associate Professor Jon Allen’s research lab has been seeking that answer.

A campus filled with history and tradition comes with boundless tall tales, passed down rumors, and unsolved mysteries. Take the Crim Dell jellyfish, for example. Some say they are real, some say they are fantasy. Some say they return yearly, while others claim they bloom in cycle. Students all over campus have conflicting iterations of the story of the Crim jellies. Let’s get one thing straight: The Crim Dell jellyfish are real. But that’s not where the mystery ends.

This species is called Craspedacusta sowerbii, the only freshwater jellyfish in the world. They are an invasive species from the Yangtze River basin in China, and have spread to every continent, except Antarctica. Their introduction to North America, dating back to 1885, was through the importation of aquatic plants. By sticking to feathers, feet, or fur of migrating animals, the microscopic polyps invade bodies of freshwater. There, they reproduce asexually, creating thousands more. The jellyfish are hydrozoans, meaning they have two stages in their life cycle: The polyp stage and the jelly, or medusa, stage. 

The first recording of jellyfish on campus was in 1949, making this year the 75th anniversary of their first spotting at the College of William and Mary. Found by a faculty member at the Virginia Institute of Marine Science in Lake Matoaka, they have been unseen since. Every other finding of the jellyfish was in the Crim Dell, where they have been known to bloom every six or seven years. “In 2019 they started showing up more regularly,” said Jon Allen, associate professor of biology and director of the Allen Lab. “Since then, I think they’ve been here in abundance three of the last five years.”

When the jellies bloom, like they have this fall, they are only around for about six weeks. Although the blooms are irregular, the polyp stage is always present in the Crim Dell. “Only some years do they make jellyfish, and in all other years, they choose not to, and we don’t understand why,” Allen explained. 

The polyps are very resistant to changes in their environment, which has ensured their survival. The Crim Dell has been drained and dredged many times for maintenance, but the polyps and jellies always return. The polyps enter a resting stage that can survive in moist land for 40 years. “You could drain the Crim Dell when you got to campus and not refill it until you were an adult and you had children of your own who came to William and Mary, and then refill it to celebrate them coming to William and Mary, and those jellyfish polyps would still be there alive,” Allen said.

The lab’s current research question is about what causes these blooms. “The mystery, I suppose, is why are they there? In tremendous numbers, like by the thousands in some years and not at all in other years,” Allen disclosed. Figuring out their drives for reproduction is key to understanding the jellyfish’s role in the Crim Dell ecosystem. “When there are these big blooms, and you get tens of thousands of jellyfish in a very small area, what does that do to the native organisms that live there?”

This is the main area of interest for student researcher Savara Shrivastava ’27. “My favorite thing, I think, is to see how they interact with other organisms and try to see, because they are an invasive species, how they’re affecting the community in both stages.” Studying the jellyfish’s behavior is especially exciting because there is a lot of controversy about their interactions with other species. After studying published research, Shrivastava noted, “There’s some literature that suggests that they could be really important in shaping how the plankton community works; there’s some literature that says they might not actually be that important at all.”

Because the jellies are an invasive species, they probably serve as competition against native species for food, so the Allen Lab studies what they eat and how much. Allen noticed the jellies had a strong preference for brine shrimp and other small crustaceans. Watching them prey on the shrimp has provided insight into their stinging abilities. The researchers drop brine shrimp into a container with the jellyfish, and once the jellies come into contact with the much larger shrimp, all it takes is three seconds before the shrimp is paralyzed and ready to eat. “The efficiency of their predatory abilities is probably the thing I think is coolest,”admitted Allen.

Not only does their powerful sting come into play when the jellies are the predator, but also when they are the prey. Shrivastava took a sample of jellyfish to the Keck Lab and fed them to native vertebrate animals found on campus bodies of water to see how they would respond to the jellyfish. The jellies were first given to turtles, which were passive and uninterested. Then, Shrivastava fed them to fish. “We had a bunch of small fish try to eat it that were about the same size as the jellies ... so they would take pecks at it and then look a little disturbed and then swim away.”

When Shrivastava tried feeding the jellies to catfish, there was a bigger reaction. “We had these catfish that were big enough to swallow them whole, and the catfish would try to swallow them and then spit them out immediately.” The jellyfish stung the catfish internally, which led to “a continuous shaking motion, very erratic movement, heavy breathing ... They were very displeased with eating a jelly.”

Another major question at the lab concerns the jellyfish’s reproduction. This year, the lab found thousands of jellies in the Crim Dell, all of which were female. Two years ago, during the last bloom, all of the jellies they found were male. The lab seeks to understand the jellyfish’s sex determination mechanism. “We don’t know if ... they need to develop in a certain temperature, like sea turtle eggs where you’ve got temperature dependent sex determination, or is it something where it’s a genetic thing,” Shrivastava said.

Another possibility is that all of the jellyfish in a bloom are clones. A single polyp might have asexually reproduced itself thousands of times, making an entire population of clones with the same genetic material, which may explain why they are all the same gender.

Passing by the Crim Dell, Shrivastava could be seen conducting field work alongside fellow lab volunteers Lexi Dyer ’27 and Sierra Hall ’27. Onlookers stopped to ask them what they are studying and if the jellies really are real or not. Seeing the public’s curiosity about the jellies, the lab started an Instagram account, @crimjells, to share their findings. “You have this really cool organism that so many people around the world are interested in, and it’s right here on campus,” Shrivastava said about expanding the lab’s communication reach. “We think that the community here deserves to know a little bit more about it.”

Being such unique and obscure creatures makes studying them an exciting puzzle. “There are so many mysteries about them, but that’s the whole point of doing science on them, is to solve some of those mysteries,” Shrivastava said. “And as you solve them, you get more questions to ask.”