Imagine you are walking along the beach under a dark, new moon sky, and you see a flicker of aquamarine out in the waves. You look around you for a flashlight, lighthouse, or even an airplane taking off that could have caused the flicker, but you find none. Again, the lapping waves rushing into shore glitter with an eerie blue, almost alien-like in the distance. But you needn’t worry that Mars has finally come to attack planet Earth — it’s just a little bioluminescent algae!
Bioluminescent algae are known for producing a vivid flash of blue-green light whenever their surroundings are disturbed, usually by something as simple as the water around them being in motion. Controlled by circadian rhythms, the light becomes visible at night, appearing along the crest of breaking waves or outlining schools of fish. It’s highly possible that they served in the past as inspiration for ghost stories; the sparkling light takes on an etheral effect when seen from far away. Large quantities of bioluminescent algae that wash up on beaches can also leave glowing footprints in wet sand.
However, mysticism aside, their beautiful appearance has a practical purpose: the flashing light, which usually lasts about 0.1 second, functions as a survival mechanism, allowing the algae to startle its predators and frighten them away. Also, the light can attract larger predators to the area, causing the algae’s own predators to flee.
The key to understanding the light produced by bioluminescent algae lies in the reaction of oxygen with the complex molecule luciferin, which releases the extra energy in the form of cold light, so called because bioluminescent algae give off almost no heat whatsoever during this process. However, the reaction would be almost useless without the presence of the enzyme luciferase.
Although luciferase is not directly involved in the reaction itself, all enzymes ensure a faster, more efficient reaction. During the day the water’s pH remains at 8, allowing luciferin to remain stable. At night the water’s pH changes to 6, causing luciferin to change its shape. Luciferase is then able to bind with the molecule, speeding up the reaction.
Curiously enough, the production of light is thought to have initially been an incidental side effect; the true purpose of oxidizing luciferin may have been to bind up excess oxygen, which can damage cells. Regardless of the science behind it, bioluminescent algae is truly one of our planet’s most fascinating phenomena.