It Really Is the Little Things in Life

The rush to understand the hidden world of marine plankton.

Published December 7, 2015

They’re unlikely little life forms to instill such passion.

Some look like monsters trapped in gelatinous barrels; others sport racks of prism-filled combs that diffract rainbows of light. They resemble translucent Eiffel towers or bring to mind spaceships, shot through with bullet holes. Taken as a group, they assume shapes so bizarre, so multifarious, that they echo the hallucinogenic visions of science-fiction writers.

They are among the earliest of earthlings: plankton.

Many are microscopic or just incredibly tiny: viruses, bacteria, algae, and cyanobacteria. They are our ancestors—and our superheroes—since their very existence underpins so much of life on Earth. Yet planktonic organisms remain largely unexamined, even as they face threats that could, in turn, threaten life as we know it. Which is why a group of scientists, led by the very passionate French molecular biologist Eric Karsenti, has launched urgent research into the life of plankton.

In 2009, Karsenti and his crew began a project to gather these neglected children of evolution. The team has already identified as many as 35,000 new planktonic species, but the more difficult and elusive objective is to determine how these tiny creatures with supersized jobs work together in global communities. If the team can do that, they may just foretell the planet’s future.

Like many great scientific expeditions, it took a boat and an ocean odyssey to find some answers.

Karsenti, 67, is an unlikely champion of plankton. A scientist with an outsized personality, famous for his unruly beard and mop of curly, snow-white hair, he has spent the better part of his career in the lab immersed in the mitotic inner workings of the cell, figuring out what triggers a cell to divide and how it knows to pass on the exact same slate of chromosomes to a daughter cell.

But almost two decades ago, Karsenti had an epiphany: the complex interactions he had spent his life unlocking within the cell had developed from interactions among far larger networks of living creatures. Therefore, to fully understand what was happening inside the cell, he needed to understand how life evolved in the first place. And that meant understanding Earth’s early inhabitants, marine plankton.

Planktonic organisms, their name derived from the Greek planktos meaning errant or wandering, drift on the ocean’s currents. Their diversity is stunning and seemingly endless and they are broadly divided into three categories: phytoplankton, the plant-like photosynthesizers (green algae, diatoms, and dinoflagellates, for example); zooplankton, the animals; and free-floating bacteria. All play critical roles in the ocean’s myriad food chains, serving as predator, prey, and/or forage. As photosynthetic organisms, phytoplankton capture carbon dioxide and release oxygen. Along with terrestrial plants, they fill the lungs of Earth. Without them, life on an oxygen-dependent planet would be no longer. So it seems crazy that only now is science focusing on plankton. The research lag, however, is understandable: few planktonic organisms can be successfully grown in a lab for in-depth study.

Karsenti’s revelation meant he had to go where most of the world’s plankton live—to the ocean. Which meant he had to find a boat. And that led him to the schooner Tara, and a journey around the world that would involve 150 scientists.

The schooner, Tara, on its journey around the world to study marine plankton. Photo by F. Latreille/Tara Expedition

Karsenti has always been a keen sailor and, like so many scientists over the ages, his imagination has been fired by the romantic seafaring quests of western scientists, including the 1,000-day expedition in the 1870s of the HMS Challenger that set the tone for modern marine biology, discovering new species and sounding the ocean’s mysterious depths; and Charles Darwin’s 1830s round-the-world voyage of nearly five years on HMS Beagle, that led him to find exotic new creatures and eventually develop his theory of evolution.

About 10 years ago, Karsenti enlisted the intellectual help of cell biologist Christian Sardet and plankton specialist Gaby Gorsky, both of the Observatoire Océanologique de Villefranche-sur-Mer, on the Mediterranean Coast of France. Together they came up with an idea and a bold 21st-century plan: a modern-day expedition that was Darwinian and necessary to unravel the story of plankton.

“There was a feeling that what was needed was to study plankton end to end, viruses to small organisms,” Karsenti says. “There was a hole there. Somehow, nobody had done it … It was a discovery of part of the universe you don’t know.”

But, embedded within Karsenti’s new plan to study plankton holistically, was a possibility yet more urgent: could the fate of plankton be linked to the fate of other species, including humans?

The idea that marine planktonic organisms are a linchpin to the planet’s fundamental operation is recent. To Darwin, who captured plankton in a net he pulled behind the Beagle, they were, at best, a scientific curiosity. He wrote on January 11, 1832: “Many of these creatures so low in the scale of nature are most exquisite in their forms & rich colours. It creates a feeling of wonder that so much beauty should be apparently created for such little purpose.”

Nearly a century later, Winfred Emory Allen, a plankton specialist at Scripps Institute of Oceanography at University of California, San Diego, had turned that view on its head, writing in 1927 that “every plankton organism is important,” if only because it is food for something else. He pleaded for scientists to study planktonic life.

The Sir Alister Hardy Foundation for Ocean Science in Plymouth, England took up the call in 1931, and has been collecting plankton samples ever since by providing fine silk nets for merchant and research ships to drag through the North Atlantic and North Sea. The goal was to use plankton samples as a measure to predict the health of the commercial fisheries in those parts of the ocean.

More recently, as computing power advanced enough to analyze massive volumes of data, the adventurer and geneticist J. Craig Venter traveled around the globe in his yacht Sorcerer II, which he called a “floating lab,” snatching up bacterial plankton and then chopping them randomly into bits to examine their genomic sequences, reporting in 2007 the discovery of 1.2 million new genes.

By the time Karsenti and the expedition crew was setting off in Tara, the 36-meter sailing ship provided by Etienne Bourgois, son of the French fashion designer agnès b., pieces of the planktonic puzzle were steadily falling into place. The expedition could pose even more pressing questions—more “hows” and “whys”—than they had originally set.

Expedition leaders, Eric Karsenti (left) and Tara owner Etienne Bourgois, son of the French fashion designer agnès b., in Patagonia. Photo by Patrick Filleux/AFP/Getty Images

Not only that, but the Tara Expedition also coincided with an emerging trend: ocean scientists were beginning to look at the ocean as a whole system and to see how it connects with other systems on the planet. While much of the long history of biology has been aimed at collecting, cataloguing, and naming organisms, the study of ecology—a discipline that examines how organisms interact with one another and their environment—rose to prominence in the latter half of the 20th century. Rachel Carson’s 1962 book Silent Spring, is an early example of the discipline.

Until very recently, ecological studies focused primarily on terrestrial, rather than marine, environments. The first major scientific papers on ocean acidification came out in 1999 and 2000. The first paper describing a global map of human effects on marine ecosystems was published in 2008. Other research looking at whole ocean systems—say, its nitrogen content or how oxygen gets moved around—is even more recent.

As Tara set off, the emerging picture was this: plankton as a connected global community rather than a sea of isolated individuals; and plankton as global workhorses, engineers of the atmosphere and climate. And it was all happening in the ocean, a watery medium that scientists were just starting to see as a global force in itself.

Perhaps more importantly, marine researchers were beginning to realize that the chemistry of the ocean is changing fast—“at a rate we almost can’t comprehend,” says Philip Boyd, an ocean biogeochemist at the Institute for Marine and Antarctic Studies in Hobart, Tasmania.

The cause: mounting carbon dioxide concentrations in the atmosphere that get soaked up into the ocean. Plankton—an understudied critical cog in the atmospheric engine—were suddenly at risk.

The changes plankton now face are fundamental ones: the ocean is becoming warmer and more acidic, and their access to nutrients, oxygen, trace metals, and light is shifting.

Each of these affects the growth and survival of different plankton in different ways. For example, as the water becomes more acidic, plankton and other creatures that make shells and other structures out of calcium carbonate have a harder time with their construction, a phenomenon that is becoming better known. Less well known is that large sections of the deep ocean far from the coastlines are becoming anoxic, making them inhospitable to most life.

The Tara Expedition stopped in Murmansk, Russia. Photo by Anna Deniaud Garcia/Tara Expedition

The consequences are chilling because, put simply, planktonic organisms are the key to life on Earth.

“We really don’t know where things are at,” Boyd says. “This is not a time for dithering. People want answers now. The stakes are high now.”

For her part, Stephanie Dutkiewicz, at the Center for Global Change Science at Massachusetts Institute of Technology and a lead plankton researcher, has been trying to determine which phytoplankton will survive in the altered ocean of the future. So far, she has found that planktonic communities will be more radically altered than she expected, mainly in response to more acidic waters. The consequences remain unclear, Dutkiewicz says.

There are some rays of hope. Dutkiewicz points to a 2012 paper describing experiments on the wildly abundant Emiliania huxleyi, or EHUX, which showed that over the course of a year—or 500 generations of this species—there was some adaptation to more acidic waters.

But she also pointed out that the swift increase in carbon dioxide content of the atmosphere and ocean is a huge, uncontrolled experiment, “horribly, horribly so.” Not all creatures can be expected to adapt to changes as rapid as those the ocean is now experiencing, as the planet’s previous five mass extinctions have shown.

The Tara Expedition research will provide scientists with some guideposts, which was gratifying for Karsenti, who really had no idea what to expect when his crew first launched. Like Darwin, he had set out expecting to find new species; and he found something more profound, new hints about how life evolved. Tara’s boldest revelations are years away as researchers continue to work with the new data. Already though, at least one discovery has provoked pure scientific excitement: the revelation that planktonic viruses routinely exchange genes opens up insight into how marine creatures interact. What else do they share? How much do they share? How does the sharing affect the balance of life in the ocean? Could creatures in the ocean be symbiotic in ways no one imagined? Even more intriguing: a number of microbes found in the human gut are also found in the ocean. What gives?

Marine plankton sampled from the Mediterranean Sea. The Tara Expedition team identified as many as 35,000 new planktonic species. Photo courtesy of the Tara Expedition

And already there are hints of what’s to come. For one, planktonic organisms appear to be far touchier when it comes to water temperature than the Tara researchers expected. A change of as little as one degree Celsius can drastically change a localized planktonic community, altering its food chain. Because the ocean has sopped up 93 percent of the extra atmospheric heat that higher carbon dioxide concentrations have trapped against the planet’s body since the 1970s, this change may have profound effects on planktonic life, with unknown consequences for all of us.

The most pressing question of all: can the ocean’s tiny, weirdly formed, shape-shifting, multi-tasking, nearly invisible guardians of the atmosphere adapt fast enough for those of us who need them to live on this planet?

Nobody knows.

At the moment, the Tara crew has tacked, shifting its current position and mission. Just as world leaders and activists began gathering in Paris this week for the United Nations Climate Change Conference, the next round of international climate action talks, the schooner lowered her sails and made her way down the river Seine, under the bridges, to dock at Pont Alexandre III, near the Grand Palais.

She will be there until mid-December, serving as a floating classroom and a platform from which to explain how high carbon dioxide concentrations in the atmosphere could have dismal effects on plankton and other living creatures. After all, say the Tara team members, the best idea is to avoid having to predict the future and curb carbon emissions now.