26 February 2023

If, like me, you live far from the ocean you may never have seen breaking waves glow blue at night. This bioluminescence is caused by single-celled organisms floating in ocean surface water whose defense mechanism creates blue light when they feel threatened.

Bioluminescence is relatively rare on land (think fireflies and fungi) but is common in the ocean where 76% of the organisms can create their own light through a chemical reaction between oxygen and the enzyme luciferase. The color is predominantly blue, the wavelength that travels furthest in water, and is a useful adaptation in the deep where sunlight cannot penetrate below 200 feet.

The glowing blue waves pictured above are created by dense populations of marine plankton called dinoflagellates. During the day they color the water red — a “red tide.”

Some are toxic but in San Diego in 2011 the organism was identified as harmless Lingulodinium polyedrum so it was safe to swim. ( Lingulodinium polyedrum might be top center below.)

Dinoflagellates automatically glow to warn off predators so when a wave begins to break and the jostling mimics a predator, the glowing begins. When the wave subsides the glowing stops. You can see the red tide of dinoflagellates in front of the blue wave below.

Watch it in action in this video from 2011.

Red tides happen fairly frequently in San Diego, though not every year, and they tend to be benign. (They are generally NOT benign in Florida!) Learn more about the 2011 bioluminescence in this video:

(photos from Wikimedia Commons and by Kevin Baird via Flickr Creative Commons license)