Jellyfish in the Bay: Nutrient Cycling and Sinking

Josh Stone. ©VIMS
Josh Stone weighing a jellyfish to determine decomposition rates. ©VIMS

By Julia Robins, Staff Writer

They’re slimy, they sting, and, at some point, they’ve probably kept you from enjoying a day at the beach. But jellyfish in the Chesapeake Bay play key ecological roles as grazers and predators and have the potential to greatly affect nutrient cycling—the movement of nutrients from the environment into living organisms and back again.

Josh Stone, a Virginia Sea Grant graduate research fellow and graduate student at Virginia Institute of Marine Science, is studying whether jellyfish populations have increased over the years and how they affect nutrient cycling in the Chesapeake Bay. He’s focusing his research on comb jellies, which don’t sting, and stinging sea nettles, which do.

Stone measuring the biovolume of a jellyfish. ©VIMS

In late spring, the comb jellies flourish, consuming aquatic bugs called copepods, larval fish, and fish eggs. The stinging sea nettles typically arrive later and eat the comb jellies. Even though the stinging sea nettles are, as Stone says, “the ones that no one likes,” ecologically they may serve an important role—regulating the comb jelly population.

“When there’s a [comb jelly] bloom out there you can’t find a copepod, and that’s important because a lot of the larval fishes eat copepods,” says Stone.

But stinging sea nettles can’t be counted on every year to keep comb jellies in check. In warmer, drier years, there are more sea nettles, but in wet, cold years, they are harder to find.

To get a better idea of how the two species interact and affect carbon in the water, Stone is setting up mesocosms—contained areas that can hold a small part of the natural environment under controlled conditions. He’s using four different treatments: mesocosms with no jellyfish, only comb jellies, only sea nettles, and both comb jellies and sea nettles.

“It would be really exciting to see a difference between those treatments,” says Stone. He’s also eager to see whether those differences will cause different amounts of carbon to reach the bottom.

Stone is interested in the movement of carbon because many animals that live on the bottom of the Bay depend on fallen carbon for food. At the same time, he’s interested in how its movement could add carbon dioxide into the air.

Carbon comes into play because small ocean animals called phytoplankton transform carbon dioxide in surface waters into an organic carbon through photosynthesis. When phytoplankton die, they often stay in the surface waters, releasing carbon dioxide back into the surface when they decompose. Carbon dioxide may remain dissolved in the water at the surface or diffuse out of water into the air, but carbon can also move to deep waters when waste or dead animals or plants sink. If such materials sink quickly, they may reach the deep sea before they decompose, preventing carbon dioxide from being released back into the atmosphere.

“Once it reaches the deep sea it can stay there for hundreds to thousands of years,” says Stone. “If it reaches the sediments it’ll stay there forever, basically.”

Stone predicts that stinging sea nettles may be large enough to contribute to nutrient sink. By consuming comb jellies, the nettles are, in effect, taking the comb jellies down with them.

Stone says that modelers in the Chesapeake Bay Program are also interested in how carbon moves in the Bay because, currently, no one knows how much carbon sinks to the bottom.

“If I can put numbers to that and show that different jellyfish population regimes change how those nutrients move around, it’ll be really important. That’s what I’m hoping for.”

Strong currents in the Bay prevented Stone from performing his mesocosm experiments last summer, so this summer he’ll try again in the Virginia Institute of Marine Science seawater lab. Stone is also working on a smartphone app that will allow the public to report where they see jellyfish around the Bay and see where other users have sighted them.

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