A natural phenomenon lit up the beaches of Southern California in May 2020. Following a red tide during the day, the crashing surf turned into a light show once the sun set. The waves crested, each breaker speckled with a frothy sparkle of blue-green light as it broke onto the sand. Delighting surfers and environmental scientists alike, the bioluminescent waves were a remarkable display of nature in action.

What Makes Bioluminescent Waves?

The glowing waves off the beaches in California were created by bioluminescence within millions of tiny dinoflagellates. As the waves moved toward the shore and broke, the churning action jostled the single-cell marine animals into action. According to Smithsonian Magazine, scientists think that bioluminescence in these tiny creatures evolved as a way of scaring off predators with a quick flash of light.

While people were taking videos of the waves rolling onto the beaches, others were experiencing it firsthand while surfing. This turbulence-induced bioluminescence has also been used to detect submarine activity.

How Do Dinoflagellates Make Bioluminescence?

Dinoflagellates, also known as phytoplankton or microalgae, create their own inner light from a chemical reaction between oxygen and a photoprotein called luciferin. The Ocean Portal Team at the Smithsonian describe how some light emitters use an enzyme called luciferase to catalyze the reaction. The resulting light is blueish-green, a short wavelength that travels further through ocean water than the longer wavelengths of red light.

Dinoflagellates don’t have a monopoly on glowing from within. Deep-sea creatures that live in the dark ocean depths create their own light sources, too. Some squid species have specialized collections of light-emitting bacteria gathered within their bodies. Angler fish dangle a light lure to attract prey, and that same prey often uses bioluminescence to signal being attacked in the hope of bringing an even bigger predator to the rescue. This feature was used to capture the first video of a giant deep-sea squid in action. In this TED Talk, researchers described using a blue light lure as an alarm to simulate predator attack.

When Does Ocean Bioluminescence Take Place?

Bioluminescent waves such as the ones seen in southern California usually happen after a red tide, as noted by Atlas Obscura, when millions of dinoflagellates or other unicellular organisms gather. The name comes from the water’s appearance during the day. Since they are like plants and contain chlorophyll, the organisms gather in great numbers on the ocean surface as they need sunlight to generate energy. The Scripps Institute of Oceanography at University of California, San Diego, describes how each dinoflagellate contains a blob of red, so that when they gather together in large numbers they turn the water red. This is usually called a bloom and can last for days, weeks or even months. For example, the red tide off the southwest coast of Florida in 2017 lasted over 10 months, as noted by National Geographic.

Red Tide Danger

Bioluminescence isn’t dangerous to humans or animals; however, red tides can pose a serious threat. The red tide that occurred in Florida in 2017 caused a massive fish die-off. Along with the smell of decaying fish that washed up on the shore, the algal red tide also released fumes that caused respiratory irritation to people on the shore.

Termed harmful algal blooms (HABs) by the National Oceanic and Atmospheric Administration (NOAA), these vast accumulations of dinoflagellates choke the water surface with their sheer mass. While it’s still not clear why HABs occur, there seems to be a link with a change in water conditions, such as when storms disrupt the water column, bringing deeper water to the surface. The Environmental Protection Agency (EPA) notes that climate change could see an increased incidence of HABs. Run-off from agriculture also contributes to HABs because it loads nutrients into areas that feed the algal bloom.

Not only can HABs deplete oxygen levels to form dead zones in the water, some algal species involved in red tides produce toxins as they grow and die off. These can be neurotoxins or irritants such as brevetoxin or endotoxin. If ingested through drinking the water or eating contaminated shellfish, they can cause serious illness and even death. Marine animals and even dogs running along affected beaches have been killed by red tides.