The science behind bioluminescent waves

Over the last few weeks beach-goers in California have been treated to a beautiful natural phenomenon, blooms of bioluminescent phytoplankton have turned crashing waves and other aquatic activities into a dazzling neon light show, but why and how is this really happening?

crashing wave
People enjoying the incredible spectacle created by tiny glowing plankton

During the last month the coastline of Southern California has been home to some vibrant visitors putting on a colourful display for local residents. The bloom of specialised phytoplankton, which have turned the normally crystal clear pacific waters a murky red, come alive at night and emit a neon blue glow when disturbed. The result has been a series of stunning bioluminescent lightshows as the microscopic creatures get caught up in the crashing waves, which has been enjoyed by beach goers, surfers and even wildlife alike. It is not the first time this phenomenon has been observed along the beaches of the golden state, but this year’s event has been unusually long and bright. So just what is actually going on inside these fluorescent phytoplankton and why do they light themselves up at all?

Surfing the ‘sea sparkle’

For the last few weeks there have probably been as many people lining the sandy beaches of California after dark as there have been during the day. All thanks to the natural bioluminescence of the phytoplankton blooms, which has been affectionately nicknamed ‘sea sparkle’ by local residents. It is most visible around two hours after sunset and has been enjoyed by swimmers, kayakers, boaters, paddleboarders and surfers, who have taken to riding the neon blue waves at night. Speaking to the Guardian, local surfers described the experience as ‘like nothing they’ve ever seen’, saying that paddling out towards the waves it was “like there was a glowstick around your hand” and that their surfboards left a “bioluminescent wake”.

 

riding wave
A surfer takes advantage of the rare chance of riding a bioluminescent wave

Thanks to the rise of social media images and videos of the glow-in-the-dark waves spread far beyond California and the US, in part to the fact that this year’s ‘sea sparkle’ was the most vibrant and colourful for over 20 years. One fisherman from Newport Beach also managed to capture footage of dolphins glowing as they swam through the blooms at night, looking more like spiritual entities than real animals (see below).

A ‘red tide’ rarity

Despite glowing a neon blue at night the name for this local phenomenon is actually ‘the red tide’ thanks to the murky red colour of the phytoplankton during the day. Unlike a lot of phytoplankton blooms this red tide is brought about by a single dinoflagellate species named Lingulodinium polyedrum. They have been periodically blooming along the coast of California from Baja to Los Angeles since 1900, and although there is no set length or pattern to the blooms this year’s event is somewhat of an outlier. Firstly as we have already seen it has been one of the brightest in living memory, but what is perhaps most unusual is the length of time the bloom has latest.

coastline
This spectacle has been seen along California’s cost for over a hundred years, but never quite like this

So far the blooms have been going on for the best part of a month with no immediate end in sight. The plankton pose no serious threat to human health or even that of the local marine wildlife, but the reasons behind why this year’s bloom is so unique is still very much of interest to scientists. Obviously with seeing unusual variations in a natural phenomenon the most obvious candidate, especially in the marine environment, is climate change impacts such as warming sea temperatures or ocean acidification. However at this moment the best guess is actually the record levels of rain that has fallen across California this winter, because the increased rainfall means there is a greater nutrient run-off from agricultural land which provides an increased source of energy for the phytoplankton to feed on.

The science behind the sparkle

The high interest in this year’s bioluminescent bloom has also peaked a lot of people’s interest in just why and how the plankton create the neon lightshow at all. To answer the why, these phytoplankton have evolved to use flashes of light as a form of predator avoidance and defence, which is done in two main ways. Firstly the intense flashes help to disrupt the feeding behaviour of predators by temporarily blinding and startling them. Secondly the light also acts as a burglar alarm, signalling to much larger predators that something they might be interested in eating is trying to eat them. In this way they are defended at night when most vulnerable to predators, allowing them to generate energy from sunlight during the day.

On the other hand, the question of how these microscopic creatures are able to generate light requires a slightly more complex answer. We know that these plankton only generate flashes when disturbed meaning that by some unknown mechanism rapid movement or detected pressure causes the flash to be emitted. What is better understood is the chemical reactions within the cell needed to create light, which involves a large reduction in pH within the cell caused by an influx of protons (positively charge sub-atomic particles) from the oxidation of a chemical known as luciferin. This chemical shift happens incredibly fast, within 20 miliseconds, and creates a short burst of visible energy that last for around a tenth of a second.

beach goers
Beach goers marvel at the sight of the bioluminescent waves

In addition to being a rapid process, it is also just a single reaction. After producing a flash of light the individual phytoplankton has spent its entirety of luciferin and will be unable to produce another until it has ‘recharged’ during the daytime hours of the next day. This means that when you are watching the magical glow of these bioluminescent waves, what you are really seeing is millions of individual plankton emitting a series of rapid single flashes, which makes the whole spectacle even more captivating.


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