Environment

What’s up with the giant jellyfish washing up on Central Coast beaches?

This moon jelly washed onto a Cayucos beach during a heavy storm in January 2018. The protrusion in the middle is its mouth.
This moon jelly washed onto a Cayucos beach during a heavy storm in January 2018. The protrusion in the middle is its mouth. mvaughan@thetribunenews.com

It’s not uncommon to find large jellyfish scattered across the beaches of the Central Coast, including on the beach that stretches from Morro Bay to Cayucos.

The large, round masses are most likely Aurelia aurita, or moon jellies — a transparent jellyfish common on the surface of the waters along the California coast.

They’re often tumbled by the ocean onto the beach during strong storms.

Moon jellies use the sun to navigate and orient, but they aren’t strong swimmers, according to George Matsumoto, a biologist with the Monterey Bay Aquarium Research Institute.

“Jellies don’t have a whole lot of control over where they show up,” Matsumoto said.

Moon jellies will be familiar to anyone who’s visited the aquarium and seen its brilliantly colored display of glowing jellies floating serenely against a deep blue background.

Those found on the beach usually don’t have any tentacles left. They’re likely rubbed off by the sand.

When they did have tentacles, they were short and fringe-like and used to sweep small plankton they’ve foraged for food toward their mouths.

Beachgoers shouldn’t be too concerned about protecting dogs and children from moon jellies. They do sting, but humans and dogs “wouldn’t even feel it,” Matsumoto said.

Brown jellies are another story, however. Their sting feels like stinging nettles, he said.

“If they start washing up, the public should stay away,” Matsumoto said.

Monica Vaughan: 805-781-7930, @MonicaLVaughan

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