Dr Rob Condon samples jellyfish from the York River. (Photo: David Malmquist,VIMS)
Jellyfish drastically change marine food webs: study
Monday, June 13, 2011, 01:40 (GMT + 9)
A new study by researchers at the Virginia Institute of Marine Science (VIMS) found that jellyfish in the Chesapeake Bay radically alter marine food webs by shifting food energy from fish toward bacteria. This impact is anticipated to climb due to an apparent increase in the size and frequency of jellyfish blooms worldwide during the last few decades.
The results of the study, led by recent VIMS PhD graduate and current faculty member at the Dauphin Island Sea Lab (DISL) in Alabama Rob Condon, appear in the Proceedings of the National Academy of Sciences.
He sampled blooms of Warty comb jellies (Mnemiopsis leidyi) and Atlantic stinging sea nettles (Chrysaora quinquecirrha) in the York River, a tributary of lower Chesapeake Bay. The researchers tracked the flow of food energy by measuring the amount of carbon absorbed and released by jellyfish and bacteria within closed containers during “incubation” experiments.
“[Jellyfish] impact food webs by capturing plankton that would otherwise be eaten by fish and converting that food energy into gelatinous biomass,” Condon said. “This restricts the transfer of energy up the food chain, because jellyfish are not readily consumed by other predators.”
Further, jellyfish shunt food energy away from the fish and shellfish that humans consume.
“Marine bacteria typically play a key role in recycling carbon, nitrogen, phosphorus and other byproducts of organic decay back into the food web,” commented 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 positive side of this is that bacteria in jelly-rich waters eventually turn carbon back to carbon dioxide instead of using it to grow larger or reproduce.
This shift toward bacterial respiration happens because jellyfish produce organic matter extra rich in carbon through excretion and the sloughing of mucus or slime, the researchers believe.
Jellyfish released copious amounts of carbon-rich organic matter—with 25 to 30-times more carbon than nitrogen versus a ratio of 6 parts carbon to 1 part nitrogen in typical marine waters. Condon said bacteria metabolized this carbon-rich material two to six times faster than with dissolved organic matter from jellyfish-free waters.
Also, the team’s research shows that an influx of dissolved organic matter from jellyfish blooms alters the make-up of the local microbial community.
“Dissolved organic matter from jellyfish favored the rapid growth and dominance of specific bacterial groups that were otherwise rare in the York River,” Condon elaborated.
Factors such as climate change, over-harvesting of fish, fertilizer runoff and habitat modifications help boost jellyfish blooms.
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By Natalia Real