Sharks or Jellyfish?



Would you rather be stuck in the middle of the ocean with a bunch of sharks or a swarm of jellyfish?

My friends and I debated this last year, and only one of my friends chose jellyfish over sharks. Jellyfish are just far scarier than sharks to me, despite movies like Jaws and the fact that news of every single shark attack spreads like wildfire.

I think I get freaked out because up to hundreds of jellyfish travel in swarms, or blooms as they’re properly known. But maybe it’s simply because sharks have eyes and a mouth that I can easily identify. Maybe it’s because dissecting a shark’s brain was the coolest part of my last biology class. Maybe it’s because the Australian box jellyfish has enough toxin in EACH tentacle to kill 60 people. In any case, I would definitely prefer a 7-foot-long Tiger shark to the giant Nomura’s jellyfish that can grow up to 6.6 feet in diameter.

  • Image of Nomura's Jellyfish courtesy of

While reports have historically emphasized the destruction caused by jellyfish swarms, a rising number of new studies have been defending the jellies including a recent article titled “Jellyfish Swarms: Menacing or Misunderstood” that brought back my memories of the debate. It recounts Monterey Bay Aquarium researcher Steven Haddock's thinking on reports of the jellyfish’s potential to overrun the seas. He believes these reports resemble monster movies and unfairly demonize the jellies. The article concludes with:

Jellyfish blooms are nothing new; these sudden proliferations of medusa are recorded in the fossil record more than 500 million years ago. "So it is hard to know if that is any different than it was a long time ago," according to Haddock.

Haddock, also a member of the NCEAS working group, said he came across a 1925 study of jellyfish reproduction, which the author speculated would help explain the masses of jellyfish that had washed up onto the beach in Monterey Bay. "Even for him in 1925, it went without saying, yeah, we get these big jellyfish blooms all the time."

It is well recognized that increasing numbers of jellyfish swarms have been causing troubles, especially in Japan, ruining fishing catches and clogging both fishing nets and power plant intakes. However, scientists are still debating how strongly human activities have contributed to this through overfishing (gets rid of natural predators), coastal construction (provides shelter for the polyp stage) and nutrient pollution (reduces oxygen and creates an all-you-can-eat phytoplankton buffet), as well as warming waters (encourages species’ expansion).

Some reports say that jellyfish may take over ecosystems while others say there has been no global impact, only local population explosions.

I suppose confusion is inevitable with the term “jellyfish” often causing misunderstanding. It is commonly used to describe an extremely diverse group of animals, from Cnidaria, with stinging cells that include the blobs you spot on beaches, to Ctenophores, comb jellies without stinging cells. Adding to the confusion is the unreliability of jellyfish population data. Groups may be up to a million one year and impossible to find the next year.

Jellyfish probably are getting a bum rap, but I still choose the sharks. What about you?

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