Over the last few years reports of jellyfish blooms around the world have been increasing. This is bad news for the marine food web, as the jellyfish are voracious predators of plankton, but are not readily consumed by other predators.

A new study by researchers at the Virginia Institute of Marine Science shows that jellyfish have a significant impact, drastically altering marine food webs by shunting food energy from fish toward bacteria.

The results of the study – led by Rob Condond – appear in this week’s Early Edition of the Proceedings of the National Academy of Sciences.

The researchers tracked the flow of food energy in the lab by measuring the amount of carbon taken up and released by jellyfish and bacteria within closed containers during “incubation” experiments of varying length. Carbon is the “currency” of energy exchange in living systems.

“Jellyfish are voracious predators,” says Condon. “They impact food webs by capturing plankton that would otherwise be eaten by fish and converting that food energy into gelatinous biomass. This restricts the transfer of energy up the food chain, because jellyfish are not readily consumed by other predators.”

Jellyfish also shunt food energy away from fish and shellfish that humans like to eat through their affects on the bacterial community. “Marine bacteria typically play a key role in recycling carbon, nitrogen, phosphorus, and other byproducts of organic decay back into the food web,” says Condon. “But in our study, we found that when bacteria consumed dissolved organic matter from jellyfish they shunted it toward respiration rather than growth.”

The upshot of this “jelly carbon shunt” is that bacteria in jelly-laden waters end up converting carbon back to carbon dioxide, rather than using it to grow larger or reproduce. This means the carbon is lost as a direct source of organic energy for transfer up the food web.

He adds that a host of factors, including climate change, over-harvesting of fish, fertilizer runoff and habitat modifications could help to fuel jellyfish blooms into the future. “Indeed,” he says, “we’ve seen this already in Chesapeake Bay. If these swarms continue to emerge, we could see a substantial biogeochemical impact on our ecosystems.”

Further Reading:
Robert H. Condon, Deborah K. Steinberg, Paul A. del Giorgio, Thierry C. Bouvier, Deborah A. Bronk, William M. Graham, and Hugh W. Ducklow
Jellyfish blooms result in a major microbial respiratory sink of carbon in marine systems. PNAS 2011 : 1015782108v1-201015782.
Virginia Institute of Marine Science