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San Diego beaches are glowing in the dark. Here's why




The waters off of San Diego glowing blue at night in May 2018. The lights are caused by rarely-occuring bioluminescent plankton tossed around by the waves.
The waters off of San Diego glowing blue at night in May 2018. The lights are caused by rarely-occuring bioluminescent plankton tossed around by the waves.
Erik Jepsen/UC San Diego

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Down toward San Diego, the ocean is glowing. For the past several days, after the sun sets, waves from La Jolla to Carlsbad have been lit up in a bright neon blue. 

"If you're in the water swimming, you see all these sparkles of light from the individual organism," says Michael Latz, a marine biologist specializing in bioluminescence at the Scripps Institution of Oceanography in San Diego.

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The cause is a rare red tide algae bloom filled with microscopic glow-in-the-dark plankton.

They illuminate as a defense mechanism against predators.

"So a predator grabs them to try and eat them," says Latz, "and they respond with a flash of light to disrupt the feeding."

But any strong force will trigger this response, including being tossed around by breaking waves.

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Researchers don't know much about the conditions that can cause this because it happens infrequently – the last instance was a week in 2013. So it's hard to predict.

When it does happen, it can be difficult for scientists to drop everything that they're currently working on to focus on it. And it's uncertain how long this current event will last.

"We're having the weather change now where it's not nice, bright and sunny," says Latz.

The lack of daylight might affect how much of that glow-in-the-dark plankton gathers near the surface.

But citizens can help out while it's here.

Latz asks that people contact him to say where they're seeing the lights and how bright they are.

"We don't know the full spatial extent of the event," he says. "I've heard it reported as far north as Carlsbad, but maybe it's further north."