Jellyfish at Ocean Beach deemed a “seasonal event” by local expert

The unexpected arrival of tens of thousands of jellyfish on Ocean Beach Saturday morning caused quite a stir throughout the Bay Area. Many of the people who flocked to the beach to observe the gelatinous blobs wanted an answer to one question: Why did the jellyfish arrive in such high numbers?

“It’s the apocalypse!” screamed one beachgoer as she flung a jellyfish at her friend.

But it was far from the apocalypse, according to Gary Williams, a researcher at the California Academy of Sciences in the Invertebrate Zoology and Geology department. In fact, he said, the arrival of the jellyfish is a “seasonal event,” fairly commonplace.

“Jellyfish cluster in massive blooms well offshore that we rarely see. But sometimes, with just the right combination of wind and currents, those blooms wash ashore.”

The size alone of Ocean Beach, along with its notorious currents, makes it a likely candidate for beached jellyfish, and moon jellies can often be spotted at Ocean Beach during the fall. While Williams acknowledged that the density of the jellyfish was unusual, it was just an extreme version of a commonplace occurrence. He remembers seeing huge amounts of jellyfish as a child along the beach at Point Reyes — another part of the Bay Area with long beaches prone to wind and shifting currents.

As for theories that Saturday’s influx of jellyfish was somehow man-made, caused either by pollution or by a depletion of the natural predators of jellyfish, Williams was skeptical.

“They are interesting theories,” he said, “but there is absolutely no evidence that this is man-made.”

The moon jellyfish, which have mostly washed away or else dried up by now, pose as no health hazard.

“And they’re not even fish,” Williams added with a chuckle. “Or made of jelly, to be honest. They’re invertebrates. They are simple creatures with no brains and no hearts. They are basic predatory invertebrates.”

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  1. Oh, sorry, there’s the photo on the one individual jellyfish, on the other story, where I saw it the first time and just forgot..
    I’m always doing stuff like this. What a dummy. OK, anyway, that’s how I roll.
    enjoying the photos … on the other story … nevermind

  2. On Saturday there was a great closeup of one of the jellyfish on this story. I loved that closeup photo! Could you put it back on this story? Please? It was awesome! (Or was I hallucinating? ) (I’m linking to this story from my little e-mail newsletter, as I, too, was awed and blown away by the jellyfish phenomenon!)–cheers

  3. At the “How Stuff Works” website, here’s an excerpt about jellyfish:

    “For example, an increase in jellyfish blooms (sudden population explosions) may signal environmental problems. In some places, blooms seem to be occurring because pollution—in the form of sewage or runoff from farms and cities—has improved feeding conditions for certain jellyfish species…..

    Some scientists have also linked jellyfish blooms to overfishing. As large predator fish disappear from an ecosystem, some scientists suspect that local jellyfish benefit from a more abundant food supply, and their populations explode. Understanding the impact of these blooms on marine ecosystems ranks as one of scientists’ most important tasks.”

    Full story here:


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