Blooms, or proliferation, of jellyfish have shown a substantial, visible impact on coastal populations – clogged nets for fishermen, stinging waters for tourists, even choked intake lines for power plants. Now, a new collaborative study suggests that what these jellyfish leave behind may alter the food chain for fisheries production as well.
A potential increase inthe size and frequency of jellyfish blooms in coastal and estuarine waters around the world during the last few decades means that jellies’ impact on marine food webs could increase into the future.
The results of the study, led by recent Virginia Institute Marine Science PhD graduate and current marine scientist at the Dauphin Island Sea Lab (DISL) in Alabama, Rob Condon, appear in the latest issue of the Proceedings of the National Academy of Sciences (PNAS, Article #2010-15782RR). His co-authors are VIMS professors Deborah Steinberg and Deborah Bronk, Paul del Giorgio of the Université du Québec à Montréal, Thierry Bouvier of Université Montpellier II in France, Monty Graham of DISL, and Hugh Ducklow of the Marine Biological Laboratory in Woods Hole, Massachusetts.
Condon conducted his field studies by sampling jellyfish blooms in the York River, a tributary of lower Chesapeake Bay (http://vimeo.com/24568131). In laboratory experiments, researchers measured the amount of carbon taken up and released by jellyfish and bacteria. 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,” or direct, food energy away from fish and shellfish that humans like to eat through their impacts on the bacterial community.
“Marine bacteria typically play a key role in recycling carbon 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.
The researchers think the shift toward bacterial respiration happens because jellyfish produce organic matter that is extra rich in carbon. They do so through excretion and the sloughing of mucus. “The mucus is the slime you feel when you pick up a jelly,” says Steinberg.
Overall, says Condon, 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. Increasing influences, like climate change, over-harvesting of fish, fertilizer runoff, habitat modifications, and other factors could help to fuel jellyfish blooms. Indeed, we’ve seen this already in many regions around the world. If these swarms continue to emerge, we could see a substantial biogeochemical impact on our ecosystems.”
“From a fisheries perspective, 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.”
|Figure showing the two species of jellyfish included in the study. The rice grain flecks inside the comb jelly are the copepod prey that are also food for fish. Also provided is an example of a moon jelly bloom in Chesapeake Bay. There are thousands of jellyfish aggregated together in surface slicks, which are typically associated with physical features in the water column, such as fronts. Similar types of aggregations of moon jellyfish have been reported elsewhere in the world, such as the Gulf of Mexico, Japan and Prince William Sound, where they cause problems for fisheries and power plants. Photo credits: Rob Condon (Mnemiopsis and Chrysaora), Scott Kupiec, Gloucester, VA (Aurelia).
PNAS Article #2010-15782RR:
“Jellyfish blooms result in a major microbial respiratory sink of carbon in marine systems" by Robert Condon et al.
**NOTE: ARTICLE IS EMBARGOED UNTIL MONDAY, JUNE 6, 2011 at 3.00PM EASTERN TIME**
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Video http://vimeo.com/24568131taken of a Mnemiopsis ctenophore bloom in the York River estuary, southern Chesapeake Bay in May 2006. This plankton tow was conducted over a two minute period in surface waters and shows the typical size of a ctenophore bloom. The slimy material is the dissolved organic matter or jelly-DOM released by the jellyfish and is also used by bacteria for respiration. Video taken by Juliette Giordano and edited by Molly Bogeberg