A new study by the researchers at the Virginia Institute of Marine Science (VIMS) revealed that jellyfish have a more significant impact than just irritating swimmers in the Chesapeake: they are drastically changing the marine food webs by shifting food energy away from fish towards bacteria.
The frequency and size of jellyfish blooms in coastal and estuarine waters over the last few decades leads the researchers to believe that the impact of jellyfish on the food web is likely to continue to increase.
The study was led by VIMS Ph.D. graduate and faculty member of Dauphin Island Sea Lab, Rob Condon, and will be published in the Early Edition of the Proceedings of the National Academy of Sciences. He co-authored the paper with VIMS professors, Deborah Steinberg and Deborah Bronk, Paul del Giorgio of the Université du Québec à Montréal, Thierry Bouvier of Université Montpellier in France, Monty Graham of DISL, and Hugh Ducklow of the Marine Biological Laboratory in Woods Hole, Massachusetts.
The study was completed by sampling jellyfish blooms in the York River and the experiments took place in labs at VIMS, and in Canada and France. They tracked the flow of food energy by measuring the amount of carbon taken in and released by the jellyfish and bacteria in closed containers.
“Jellyfish are voracious predators,” said 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.”
“Marine bacteria typically play a key role in recycling carbon, nitrogen, phosphorus, and other byproducts of organic decay back into the food web,” explained 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 good news is that the bacteria in jelly-filled waters end up converting the carbon back to carbon dioxide, instead of using it to grow larger.
The research team believes that the shift towards bacterial respiration happens because jellyfish produce carbon-rich organic matter. This happens through excretion of mucus. “The mucus is the slime you feel when you pick up a jelly,” explains Steinberg.
The jellyfish of this experiment released large quantities of organic matter with 25 to 30 times more carbon than nitrogen. The typical carbon to nitrogen ratio is only six to one.
“The bacteria metabolized this carbon-rich material two to six times faster than they did with dissolved organic matter from water without jellyfish,” said Condon. “This rapid metabolism shunted carbon toward respiration rather than production, reducing their potential to assimilate this material by 10 to 15 percent.”
Steinberg explains that the dissolved organic matter (DOM) from jellyfish “just doesn’t provide an efficient food source for marine bacteria.” This dissolved organic matter also changes the composition of local microbial communities.
“Dissolved organic matter from jellyfish favored the rapid growth and dominance of specific bacterial groups that were otherwise rare in the York River,” said Condon. “This implies that jelly-DOM was channeled through a small component of the local microbial assemblage and thus induced large changes in community composition.”
Condon explains that the team’s findings “suggest major shifts in microbial structure and function associated with jellyfish blooms, and a large detour of energy toward bacteria and away from higher trophic levels.” He also adds that climate change, unsustainable fishing, fertilizer runoff, and habitat changes could also fuel jellyfish blooms in the near future.
“Simply knowing how carbon is processed by phytoplankton, zooplankton, microbes or other trophic levels in space and time can lead to estimates of how much carbon energy is available for fish to consume,” he said. “The more we know, the better we can manage ecosystem resources.”
Copyright © 2011 by Marine Science Today, a publication of OceanLines LLC