Swimming in the Light at Night

 

When I was still attending UCSD in La Jolla, CA, a group of us from the dorms had an impromptu bonfire at La Jolla Shores. From the fire we could see the waves glowing in the dark and one woman and I decided to go out into the water and see the phenomena up close. From a distance there was a diffuse glow, but up close it resolved into a constellation of glowing points of light that lit up when disturbed, outlining my legs and arms. I could make out the fish here and there around us that were outlined in glowing clouds of stars.

That detail—where a smooth, distant glow separates into individual sparks of light tracing the motion of skin and sea life—captures the exact reality of a bioluminescent red tide off La Jolla.

Bioluminescent waves breaking along the shore.. Source: Kevin Key / Slworking / Getty Images

What you experienced was a bloom of dinoflagellates (most commonly Lingulodinium polyedra along the Southern California coast). These single-celled plankton contain a light-emitting compound called luciferin and the enzyme luciferase.

When the organisms experience mechanical stress—such as a breaking wave, a moving limb, or a fish darting through the water—shear force triggers a voltage-gated proton movement across their cell membranes. This rapid chemical reaction produces a flash of blue light lasting just a fraction of a second:

• From a distance: Millions of microscopic flashes fire simultaneously in the tumbling surf, creating the illusion of a continuous, ethereal neon ribbon.

• Up close: The agitation is granular. Moving an arm or leg creates local fluid turbulence, causing the individual plankton touching your skin to ignite, effectively painting your body in a temporary silhouette of light.

• Around marine life: A fish swimming through the water leaves a wake of mechanical shear, causing the plankton to ignite along its path and rendering the fish visible as a moving comet of sparks.

It is one of the rare moments where the mechanics of marine biology produce something that feels entirely mythical—stepping into a world where every movement leaves a luminous trail in the dark.