June 8, 2009 -- Giant jellyfish like this one are taking over parts of the world's oceans as overfishing and other human activities open windows of opportunity for them to prosper, say researchers. In this photo, a diver is attaching a sensor to track a monster Echizen jellyfish, which has a body almost 5 feet across, off the coast of northern Japan. Jellyfish are normally kept in check by fish, which eat small jellyfish and compete for jellyfish food such as zooplankton, researchers said. But, with overfishing, jellyfish numbers are increasing. These huge creatures can burst through fishing nets, as well as destroy local fisheries with their taste for fish eggs and larvae. Anthony Richardson of CSIRO Marine & Atmospheric Research and colleagues reported their findings in the journal Trends in Ecology and Evolution to coincide with World Oceans Day. They say climate change could also cause jellyfish populations to grow. The team believes that for the first time, water conditions could lead to what they call a "jellyfish stable state," in which jellyfish rule the oceans. The combination of overfishing and high levels of nutrients in the water has been linked to jellyfish blooms. Nitrogen and phosphorous in run-off cause red phytoplankton blooms, which create low-oxygen dead zones where jellyfish survive, but fish can't, researchers said. "(There is) a jellyfish called Nomura, which is the biggest jellyfish in the world. It can weigh 200 kilograms (440 pounds), as big as a sumo wrestler and is 2 meters (6.5 feet) in diameter," Richardson said. Richardson said jellyfish numbers are increasing in Southeast Asia, the Black Sea, the Gulf of Mexico and the North Sea. Photo credit: Yomiuri Shibun/AFP/Getty Images
Giant jellyfish are flooding into the Sea of Japan.
The translucent creatures can grow as large as 6 feet in diameter and weigh 450 lbs. Over the last 5 years, millions have migrated from the coast of China into Japanese waters. Scientists believe they're floating in on ocean currents warmed by global climate change. The jellyfish are so heavy they rip the nets of Japanese fishermen and their venom poisons the rest of the catch. The country's fishing industry has been devastated. But a Japanese entrepreneur has decided to make lemonade out of these marine lemons. Kaneo Fukuda calls himself "Jellyfish Fukuda" and he claims to have developed more than 20 products made out of the jellyfish. He's marketing everything from makeup to mixed drinks. Anyone for a Jellyfish Sour? Are aliens attacking the Sea of Japan? Not exactly. But these gigantic blobs are unwelcome visitors from another place. Called Nomura's jellyfish, the wiggly, pinkish giants can weigh up to 450 pounds (204 kilograms)—as heavy as a male lion—and they're swarming by the millions.
The supersize sea creatures—normally found off the coasts of China and North and South Korea—occasionally drift east into the Sea of Japan to feed on tiny organisms called plankton. But now one hundred times the usual number of jellyfish are invading Japanese waters. And local fishermen are feeling as if they are under siege.
The fishermen's nets are getting weighted down, or even broken, by hundreds of Nomura's. The jellies crush, slime, and poison valuable fish in the nets, such as the tuna and salmon that the fishermen rely on to make a living.
No one knows for sure what's causing this jellyfish traffic jam. It's possible that oceans heated by global warming are creating the perfect jellyfish breeding ground. Another theory is that overfishing has decreased the numbers of some fish, which may allow the jellies to chow down without competition for food. For now, all the fishermen can do is design special nets to try to keep the jellies out. Some of them hope to turn the catastrophe into cash by selling jellyfish snacks. Peanut butter and jellyfish, anyone?
* Baby Nomura's jellyfish change from the size of a grain of rice to the size of a...
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