Jellyfish Swarms Invade Ecosystems Out of Balance

At least 150 million people around the world are exposed to jellyfish every year, the report says. Swarms of stinging jellyfish and jellyfish-like animals are transforming many world-class fisheries and tourist destinations into "jellytoriums" that are intermittently jammed with the pulsating, gelatinous creatures.

This is happening in U.S. waters from Hawaii to the Chesapeake Bay, where 500,000 people are stung by jellyfish every year.

Another 200,000 people are stung every year in Florida, and 10,000 are stung in Australia by the deadly Portuguese man-of-war, according to the report.

These jellyfish explosions are generated by human activities, some scientists believe. Possible causes include pollution, climate change, introductions of non-native species, overfishing and the presence of artificial structures, such as oil and gas rigs.

Jellyfish swarms have damaged fisheries, fish farms, seabed mining operations, desalination plants and large ships, and they have disabled nuclear power plants by clogging intake pipes.

Dense jellyfish swarm in the Gulf of Mexico (Photo by Monty Graham)

"I'm often asked whether a single, overarching condition is triggering jellyfish swarms in diverse locations," says Monty Graham of Alabama's Dauphin Island Sea Lab on a barrier island in the Gulf of Mexico. Graham says the abnormally large, dense or frequent jellyfish swarms are "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 vulnerable to opportunistic diseases, stressed ecosystems are vulnerable to infestations of jellyfish.

"There is clear, clean evidence that certain types of human-caused environmental stresses are triggering jellyfish swarms in some locations," William Hamner of the University of California at Los Angeles says in the report.

These 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; and increases in water temperatures, which accelerate the growth and reproduction of many jellyfish species.

As prey, jellyfish are eaten by seabirds, salmon, sun fish, turtles and other gelatinous creatures.

But as marine turtles have disappeared, jellyfish have proliferated. All seven species of sea turtles eat jellyfish and all seven species are endangered. Their survival is threatened by fishing lines that trap them, pollution, beach development, climate change and sales of turtles and turtle parts.

Box jellyfish in Hawaii (Photo courtesy Waikiki Aquarium)

Jellyfish are not all bad - scientists are identifying ecological services provided by the gelatinous creatures. For instance, recent studies show that the tentacles dangling from the Bering Sea's large jellyfish provide hiding places for young pollock that are pursued by other predators but have grown too big for the jellyfish to eat.

Most species of jellyfish and jellyfish-like animals are not harmful to people, according to the National Science Foundation report. But it warns that all true jellyfish and some species of jellyfish-like creatures sting - and a single stinging tentacle may be studded with thousands of stingers.

Stinging gelatinous creatures cause various reactions in people, ranging from no noticeable sensation to rashes, and some cases, death.

Australia's beaches host many types of toxic gelatinous animals, including the Portuguese man-of-war and the world's most venomous animal, the Chironex fleckeri, which can kill a person in under three minutes. In addition, the potentially deadly Irukandji jellyfish, currently increasing in number, are small enough to slip through nets that protect Australia's beaches from the larger Chironex.

Beware, warns the report. Gelatinous creatures that are harmful to people live in every ocean.

Click here to view the report, "Jellyfish Gone Wild: Environmental Change and Jellyfish Swarms."

Copyright Environment News Service (ENS) 2008. All rights reserved.