Red tide spawns blue light show at night on San Diego coastline

Find a dark spot on the San Diego County coastline after nightfall and you might be treated to a spectacular neon-blue light show.

Bioluminescent waves, glowing electric blue as they crash ashore, have been dazzling nighttime beach visitors this week. People have been snapping photos of the otherworldly surf as it has increased in intensity over the last few days.

The blue glow is caused by an algae bloom commonly referred to as a red tide. The organisms, phytoplankton called Lingulodinium polyedrum, have bloomed since late August, turning the water brownish-red in the daytime, according to UC San Diego scientists.

The churning of the waves turns the tide a brilliant blue, visible only at night.

It’s caused by a chemical reaction on the cellular level, said Peter J. Franks, a Scripps Institution of Oceanography professor who calls the phytoplankton “my favorite dinoflagellate.”

“Why favorite?” Franks wrote in a Q&A posted on the blog Deep-Sea News. “Because it’s intensely bioluminescent. When jostled, each organism will give off a flash of blue light created by a chemical reaction within the cell. When billions and billions of cells are jostled — say, by a breaking wave — you get a seriously spectacular flash of light.”

Although it is hard to predict how long the light show will last, experts say it could continue for several more weeks or months.

The algae produces a mild toxin that can accumulate in some sea creatures, but the water is safe to swim in, UC San Diego experts said, although increased ear and sinus infections have been reported during blooms.

The striking surf has awed nighttime visitors to the San Diego-area shoreline, some of whom have posted photos online.

The glowing images have lighted up blogs and social networks. Kevin Baird, who posted a photo of the bioluminescent surf on his Twitter feed, described it as “SpongeBob’s aurora borealis.”

One family at Tamarack Beach in Carlsbad was collecting the seawater in bottles to generate a similar effect described in the North County Times. “If you dump the bottles in the toilet and turn off the lights, it will light up the whole bowl,” Duane Collings of Oceanside told the newspaper. “It’s a trip.”

tony.barboza@latimes.com