Bioluminescent Algae: Definition, Causes, and Toxicity

Bioluminescent algae are a group of tiny marine organisms that can produce an ethereal glow in the dark. While the phenomenon may occur in any region or sea depth, some of the most stunning instances happen on the water's surface when the algae come close to shore, sparkling with the movement of the waves or through the jostling of boats. 

The algae's bioluminescent glow is a natural defense mechanism; light flashes occur when the algae’s environment is disturbed. Single-cell algae called dinoflagellates are almost always behind this kind of surface luminescence. The species is notorious for forming some of the most widespread bioluminescent algal blooms, but these blooms—although beautiful— are harmful to the environment and can be dangerously toxic.

What Is Bioluminescence?

Bioluminescence is light produced by a chemical reaction in a living organism. It's found in several marine animals, from bacteria and jellyfish to crustaceans and starfish. According to the U.S. National Oceanic and Atmospheric Administration, 80% of the animals living between 656 and 3,280 feet below the ocean surface are bioluminescent. Scientists previously believed that bioluminescence evolved a handful of times in ray-finned fish, but modern-day research on marine life suggests the ability arose independently 27 separate times beginning at least 150 million years ago.  

The chemical reaction responsible for this light energy has to do with a luciferin molecule, which produces light from the organism’s body when it reacts with oxygen. While there are different types of luciferins depending on the animal, some species also produce a catalyst called luciferase that helps speed up the chemical reaction. 

Bioluminescence is typically blue but can also be yellow, purple, or red. In the deep sea, bioluminescence is used as an advantage to help organisms find food, assist in reproduction, or, as is the case with bioluminescent algae, serve as a defense. Bioluminescence isn’t reserved for marine life by any means, either. Fireflies are probably the most well-recognized organisms that use bioluminescence, to warn off predators and attract mates.

Causes of Bioluminescence

The bioluminescent color produced by this chemical reaction is a result of the specific arrangement of luciferin molecules. Dinoflagellates produce their blue light using a luciferin-luciferase reaction, which is related to the chlorophyll chemical found in plants. The chemical reaction occurs between the luciferase enzyme catalyst and oxygen when the algae are jostled while suspended in water. Oxygen oxidizes the luciferin molecules, while luciferase accelerates the reaction and releases excess energy as light without generating heat. The light’s intensity, frequency, duration, and color vary depending on the species.

Southern California experiences “red tide” caused by the Lingulodinium polyedrum organism, a type of dinoflagellate algae, every few years. The waters around San Diego turn rust-colored during the day, but, any movement at night (whether by the natural jostle of the waves or a gliding boat) causes the algae to emit its signature bioluminescent glow.

The rare phenomenon of glowing oceans occurs in other parts of the world too. Three bioluminescent lagoons in Puerto Rico have algae to thank for their glow, though Fajardo's Laguna Grande has suddenly stopped glowing. Some places known for their glowing conditions can't attribute algae as the cause, such as the famed Toyama Bay in Japan; the water here gets its glow from phosphorescent creatures called firefly squids, which flock to the bay during the summer to breed.

Environmental Impact of Bioluminescent Algae

When species of bioluminescent algae like dinoflagellates become widespread and frequent, harmful algal blooms can occur. Of the 17 dinoflagellate toxin classes, two are produced by bioluminescent species, one of which has been extensively studied. Most scientists agree that both bioluminescence and toxicity function as grazing deterrents, helping the algae to ward off predators. Interestingly, in some species, both bioluminescent and non-bioluminescent strains exist.

Enough microscopic algae can “bloom” into large, dense patches on the water’s surface. Toxic algae blooms appear reddish brown (hence the nickname “red tide”) in daylight and sparkly blue at night. When larger fish and filter-feeding shellfish consume toxic bioluminescent algae in high concentrations, they can pass toxicity to marine mammals or humans when eaten. Dangerous levels of toxic algae can cause skin irritations, sickness, or even death.

In the summer months, for example, Taiwan's Matsu Islands produce large amounts of bioluminescent algae known as “blue tears.” Studies have found that toxic algae blooms in the East China Sea are growing bigger every day. In 2019, scientists connected the blue tears phenomenon to poisoned sea life as the algae release ammonia and other chemicals as they feed. Destructive algae were found as far as 300 kilometers offshore, suggesting the blooms are spreading. The researchers theorized that the bloom was driven by the construction of the Three Gorges Dam on the Yangtze River.