The ocean blue: Bioluminescence glows along Sunset Cliffs

The blue glow seen lighting up the nighttime surf recently at Sunset Cliffs and other spots along the San Diego County coast is bioluminescence, a natural light show produced by tiny organisms.

In addition to Sunset Cliffs, the phenomenon has been particularly dramatic at Ocean Beach, the Scripps Pier area of La Jolla, Cardiff-by-the-Sea and off the San Elijo State Beach campgrounds.

Bioluminescence expert Michael Latz, a scientist at the Scripps Institution of Oceanography at UC San Diego in La Jolla, said in an April 28 post on the institution’s website that bioluminescence is caused by a “red tide,” a bloom of microscopic phytoplankton with a reddish-brown color. On sunny days, the organisms swim toward the surface, where they concentrate, resulting in an intensified coloration of the water. At night, when the phytoplankton are agitated by waves or other movement in the water, they emit a neon blue glow.

Latz said local red tides have been known since the early 1900s. Several Scripps scientists are sampling the current red tide to learn more about the organisms’ characteristics, he said.

The duration of red tides varies, he said. Previous events have lasted a week to a month or more.

Bioluminescent displays are viewed best at a dark beach at least two hours after sunset. Though local beaches in San Diego County have reopened for some uses, coronavirus-related restrictions still prohibit gathering, standing or sitting on the beach. But bioluminescence also can be seen from roadways and coastal bluffs. ◆