Bioluminescent Tides Sparkle Waters

In 1688, during a scientific expedition to the Kingdom of Siam, French missionary Guy Tachard stood at the stern of his ship, captivated by millions of mysterious blue lights that glowed beneath the dark sea in his vessel’s wake.

These ghostly shimmers had long bewitched ancient seafarers, whose accounts of dolphins leaving luminous trails or of oar strokes causing water to spark like fire date as far back as 500 BC. Across Scandinavian, Polynesian, and Siberian cultures, the mythos of maritime folklore attempts to ascribe bioluminescence, or the creation of light by living organisms, to the influence of gods and monsters.

As a Jesuit priest, Tachard sought a spiritual explanation. He reasoned that the sun had “impregnated and filled the sea during the day with an infinity of fiery and luminous spirits,” and that beneath the waters, “spirits after dark reunite to pass out in a violent state.”

In reality, the mystical blue scintillae scattered like stars across the ocean’s surface are a type of microbial, single-celled phytoplankton called dinoflagellates.

The phenomenon observed by Tachard from the decks of his ship occurred within the organelles of these tiny plankton when an enzyme called luciferase–rooted in the name Lucifer, or “light-bringer”–catalyzed a reaction between oxygen and the pigment luciferin and produced a burst of photons.

Dinoflagellates light up when disturbed by motion, illuminating anything that passes through the surrounding waters. Scientists believe that this bioluminescent response may be a defense mechanism that could manifest itself in two possible outcomes. First, the bright flash of blue light may serve to intimidate, frighten, or confuse predators, much in the same way a squid deploys its ink before making an escape. Alternatively, the light may act as a beacon that calls upon a second, larger predator to come devour the dinoflagellate’s initial attacker.

The best known among the dinoflagellates is a flashy little phytoplankton called Noctiluca scintillans, which has earned itself the aptly flamboyant nickname Sea Sparkle. N. scintillans is responsible for some of the planet’s most stunning natural light displays, from the glimmering beaches of the Maldives to the famous bioluminescent bays of Puerto Rico.

Like any plant, these phytoplankton require nitrogen and phosphorous in order to grow. The amount of chemical nutrients available in the water places natural limitations on population size. However, when excess nutrients run into the ocean from chemically polluted shorelines, dinoflagellates experience an unbridled opportunity for growth and form algal blooms.

These explosions in population, commonly referred to as “red tides,” can have devastating effects on surrounding environments by depleting oxygen levels to the extent that water can no longer host marine wildlife. Many dinoflagellates also produce intensely powerful neurotoxins that kill off fish and invertebrates, or that render the creatures that eat them poisonous to humans.

Earlier this year, N. scintillans made global headlines when it formed a spectacularly luminescent algal bloom in response to chemical runoff from farms near Hong Kong. Although N. scintillans does not itself produce any toxins, its penchant for devouring other plankton whole causes it to accumulate and subsequently excrete toxic amounts of ammonia that could function as a killing agent.

Dinoflagellates may be the most common source of bioluminescence in the ocean, but they are far from being the only stars in the underwater cosmos. Given that sunlight transmits poorly in seawater, the vast majority of the oceans are bathed in utter darkness. To compensate, an estimated 80 to 90 percent of marine creatures have evolved the capacity to generate light using their own bodies.

Despite the overwhelming presence of twinkling and glimmering creatures in the deep, their existence and behaviors remain enigmatic due to the basic inadequacy of submersible equipment. Until recently, scientists were unable to observe animals in the depths without frightening them with bright lights and noisy thrusters.

Dr. Edith Widder, CEO and Senior Scientist at the Ocean Research and Conservation Association (ORCA), sought to remedy this impediment to research by developing a new technology that enables researchers to watch deep-sea creatures unobtrusively in their natural habitat. The system, called the Eye-in-the-Sea, makes use of ultra-sensitive, carefully calibrated red lights and comes equipped with an optical lure that imitates a bioluminescent display.

Widder first deployed the Eye-in-the-Sea in 2004 in the northern reaches of the Gulf of Mexico. The location she selected cradles an underwater brine pool that she suspected might act as an oasis for large predators. As hoped, during the first stage of the mission, fish swam around the camera completely unperturbed by its presence.

“I felt like I had a window into the deep sea for the first time,” Widder tells BTR, “and I could see what was going on down there without disturbing it.”

At the four-hour mark, the electronic optical lure was programmed to turn on for the first time. Within 86 seconds of its activation, Widder recorded video of a six-foot-long squid that had previously been undiscovered, and which later, experts at the Smithsonian were unable to place in a scientific family.

“It was an amazing proof of concept that there are things down there that we don’t know anything about,” she says. “We’ve explored very little of the ocean, actually. I think there are fantastic discoveries yet to be made.”

Widder resigned from her post of 16 years at Harbor Branch Oceanographic Institution and founded ORCA after she read reports that detailed the deterioration of the oceans. She was horrified to think that humans could actually be destroying the oceans before ever really knowing what lives in them. Since then, she has dedicated her career to engineering technical solutions to marine conservation challenges and paved the way for research in bioluminescence, which she believes is one of the most important processes in the ocean.

“I’ve been lucky enough to make some thrilling discoveries about who was making all that light and why, and also about what a useful tool bioluminescence is for figuring out how animals are distributed in the ocean and for monitoring the health of marine ecosystems,” she told PBS.

Widder is now working with other scientists to track pollution in the environment using the bioluminescence of bacteria.

“The bacteria allow us to create pollution maps that show us where the hot spots of toxicity are,” she explains. “Then we can work towards mitigating that.”

Featured image courtesy of Sander van der Wel.