It wasn’t man-made lights along a seaside boardwalk that caused this glow in late April and early May. This light show on Southern California and northern Mexico’s Pacific shores was all natural. The bright blue gleam in the crashing waves was caused by bioluminescent plankton tumbling in the surf.
The affected section of the Pacific experienced an algal bloom commonly called “red tide.” By day, the algae, which are a type of phytoplankton, give the water a rusty orange appearance. But at night, they glow neon blue. The phenomenon was a nighttime gift to evening beachgoers—but sadly, with beaches mostly closed, not so many were able to enjoy the rare event. Law enforcement quickly dispersed the crowds that did try to gather. With beach parking areas closed, cars congested roadways along the shoreline, creating potentially dangerous traffic situations. Officials also worried that large groups of spectators might increase transmission of the novel coronavirus.
Surfers did get to enjoy the glow up close as they took advantage of the waves at the beaches of San Diego. There, swimming, surfing, and paddleboarding were all allowed activities despite the stay-at-home orders. Dolphins and sea lions were spotted leaping and diving in the midst of the bloom, churning up the water and causing the algae to flash and sparkle with colored light with each splash and dive.
What makes the algae glow? The microscopic organisms contain chemical molecules called luciferin. The glow may be a defense mechanism for the plankton. When water is turbulently churned up—as it might be if a predator descended on the algae—the algae expends precious energy to release an enzyme called luciferase. When luciferase, luciferin, and oxygen all meet up, a chemical reaction occurs and heatless light results. Scientists speculate that the flashes of light might startle would-be predators, causing them to turn away from the glowing plankton.
Sometimes red tide algae blooms are toxic to other marine life. But that’s not the case with this one, which stretched from Baja California as far north as Los Angeles. This bloom was dominated by a phytoplankton called Lingulodinium polyedra, or L. poly for short. It is a nontoxic alga, even when it is as prolific as this one.