Jellyfish Gone Wild — Text-only | Flash Special Report
The Sea Stings Back

THE SEA STINGS BACK: ARE PEOPLE CAUSING GLOBAL INCREASES IN JELLYFISH?

HOW PEOPLE PROMOTE JELLYFISH SWARMS
“We don’t worry about the normal swarms; you just learn to live with them or avoid them,” says William Hamner of the University of California at Los Angeles. “We worry about the plagues of jellyfish that really take over an area. A jellyfish swarm is considered abnormal if it is bigger or denser or occurs more frequently than normal swarms,” says Hamner.

“I’m often asked whether a single, overarching condition is triggering jellyfish swarms in diverse locations,” says Monty Graham of the Dauphin Island Sea Lab. In response, Graham usually explains that he regards abnormally large, dense or frequent jellyfish swarms as “a symptom of an ecosystem that has been tipped off balance by environmental stresses.”

“The exact nature of such balance-tipping environmental stresses may vary from place to place and usually involve unique interactions with local ecology,” Graham explains. “But such stresses are often caused by people.”

So, just as a weakened person is particularly vulnerable to opportunistic diseases, stressed ecosystems are particularly vulnerable to infestations of opportunistic jellyfish. Nevertheless, some stressed waters do remain free of jellyfish blooms.

DEFINING HUMAN IMPACTS
“There is clear, clean evidence that certain types of human-caused environmental stresses are triggering jellyfish swarms in some locations,” says Hamner. These types of environmental stresses include:

· The introduction of jellyfish species into non-native habitats by ships;

· The formation of ultra-polluted areas, known as Dead Zones, where jellyfish face few predators and competitors;

· Increases in water temperatures, which accelerate the growth and reproduction of many jellyfish species;

Nevertheless, various constraints often complicate efforts to define human impacts on jellyfish populations in areas that are simultaneously experiencing multiple stresses, such as rising temperatures and pollution. In addition, many areas lack long-term historical records of the sizes and frequencies of jellyfish blooms and the species involved in them. Such data gaps often make it difficult to identify deviations from normal, baseline jellyfish conditions.

To address these and other constraints on jellyfish research, scientists are currently developing many new tools.These tools include: 1) computer models that are helping to identify the individual impacts of overlapping environmental stresses; and 2) DNA analyses that may help reveal the history and global movements of jellyfish species.

CAN WE EVER UN-RING THAT (JELLYFISH) BELL?
When jellyfish populations run wild, they eat large volumes of fish eggs and larvae and thereby limit the ability of fish populations to rebound. Therefore, once jellyfish dominate a stressed ecosystem, they may continue to control or influence it indefinitely.

Because of this principle, the comb jelly--a voracious, rapidly-reproducing jellyfish-like creature -- will probably maintain its tentacled-grip on Narragansett Bay indefinitely. Likewise, the comb jelly is probably now a permanent influential resident of the Black Sea--a highly stressed water body where comb jellies exploded from 0 pounds to about one billion pounds in less than 10 years during the 1980s.

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Caption/Credit:

MARVELING AT MASTIGIAS JELLYFISH
A marine lake in Palau. Credit: Dr. Jamie Seymour, James Cook University

LIVING IN THE DEAD ZONE
Draining the U.S.’s heartland, the Mississippi River dumps huge volumes of pollutants into the Gulf of Mexico. This process triggers the formation of an ultra-polluted, oxygen-starved Dead Zone in the Gulf’s bottom layers every summer. Unlike almost all other types of animals, jellyfish thrive in the Dead Zone. Every fall, seasonal storms mix oxygen-poor waters with oxygen-rich surface waters bringing a reprieve until spring. Credit: Robert Simmon, NASA