Take a drop of ocean water. Just a simple drop of water, you may think? You’d be wrong. That tiny drop is actually full of life. When one thinks about marine life, one has often in mind fish or whales or dolphins … but these only represent 2 percent of the oceans’ living organisms. The other 98 percent is made up of micro-organisms of all kinds whose generic name is plankton. Now, you may remember that, as a child, you were taught that plankton is a whale’s favorite meal. Forget about the whales. Plankton is much more than that; it is about life on Earth itself. First, because without them, we as human beings would not be here; and second, because without them, we’d probably disappear. So we’d better be aware of what happens to them, including what we do to them.

This is the reason why a French schooner called Tara spent two and a half years from September 2009 to March 2012 sailing around the globe: to provide scientists with more information on the current status of this invisible world that populates the oceans. It represented 938 days of sailing in total, 62,000 miles travelled, 32 countries visited and 126 scientists from different nationalities and all kind of disciplines – genomics, biology, oceanography, biophysics, genetics, biogeochemistry and biogeography – taking turns on board to collect more than 30,000 samples of plankton.

Chris Bowler is one of the scientific coordinators of the Tara Oceans expedition who spent some time on board the Tara. A British scientist, currently director of research at the National Centre for Scientific Research (CNRS) in France, he devotes his life to studying marine micro-organisms. When he speaks about them, it feels as if he were opening a door right in front of you to an entirely new world. He knows how to explain in a vivid and lively manner why plankton is vital for the survival of human beings on Earth. He takes you to the most fascinating journey of micro-organisms to illustrate the vital role they have played in the past and will continue to play for our future.

“Plankton has done incredible things in the past,” he starts. “These tiny living organisms, when they die, sediment at the bottom of the oceans. With time, the accumulated sediments generate different kinds of rocks like limestone, chalk and opal. We now find rock structures all over the world composed of billions of these microscopic organisms, such as the white cliffs of Dover in England, or the Sisquoc formation in Lompoc, Santa Barbara. Most of northern Europe is actually of planktonic origin.” Incidentally, this is also how fossil fuels like oil were formed: through the sedimentation over millions and millions of years of dead micro-organisms to the ocean floor.

Not only that: “Plankton also generated the air we breathe,” Bowler goes on. “Through photosynthesis, these micro-organisms took the carbon dioxide (CO2) from the atmosphere and learned how to fix it. This is how oxygen was originally generated on Earth. And this is what permitted the emergence of more complex forms of life, like animals and humans.” In other words, without oxygen-producing plankton, humans would never have seen the light of day.

Tiny, but important

But what exactly are these microorganisms?

“Well,” Bowler explains, “there are different sorts. First, we have what we call the protists, mainly the phytoplankton, if you want. There are up to 10 million of them in every liter of seawater. Then we have the metazoans, like the zooplankton, which graze on the protists. We also have bacteria – up to 1 billion/liter – and viruses – up to 10 billion/liter. These viruses are not dangerous for human beings, only for the phytoplankton and the zooplankton. They have an important regulatory role because they maintain the turnover in the system. Nature does not tolerate excess, it likes equilibrium between species. This means that as soon as one species becomes dominant, nature finds a way to eliminate it.”

The only exception to that rule of nature is … man. Although it is obvious that man has become largely dominant on Earth and has done huge damages to other species and to life on Earth itself, nature has not managed to keep up and has not – yet? – found a way to eliminate him. But “through our pollution, our destruction of the environment and our burning of fossil fuels, we are busy with it ourselves,” Bowler comments. “For despite the huge insult men have done to Earth, most life will go on regardless, one way or another. The species that is most at risk is us. So what we are actually busy doing is killing ourselves.”

Today, marine micro-organisms still play two vital roles for the survival of human beings. First, and this is probably the most obvious one, they are at the base of the food chain. They provide food to the fish which we eat. Second, they still generate half of the oxygen on the planet, removing CO2 from the atmosphere in the process. We know why this is so important: Carbon dioxide, being a greenhouse gas, is contributing to the global warming of the Earth. Hence the importance of reducing its presence in the atmosphere. “That forests are the first lung of our planet is well-known; what is much less known is that oceans constitute the second. It is like an invisible forest in the oceans,” says Bowler.

How does plankton do that?

“Micro-organisms suck in the CO2 from the air and create organic carbon to grow and proliferate,” Bowler explains. “And when they die, some of them sink to the bottom of the oceans, taking this carbon dioxide with them. This is what is called the carbon pump and it is one important way of taking CO2 out of the atmosphere. And the bigger these micro-organisms are, the easier and the faster they sink to the bottom. In other words, the heavier they are, the more effective they are in taking CO2 down to the ocean depths.”

This means that if pollution or other human activities lead to the extinction of the big guys and they are replaced by a lot of smaller ones, these will be less effective in taking the carbon dioxide down to the bottom of the ocean. And so global warming may accelerate as a consequence.

Changes in these unique ecosystems could therefore have enormous consequences for life on our planet. And this is why the work done by the Tara Oceans expedition is so important.

“What we are trying to understand is how these ecosystems work and interconnect: Who cooperates with whom, who kills whom? Why are they built as they are? What is their reaction to a change in temperature, in acidity of the water? What is the impact on them from climate change, from shipping, from overfishing, from pollution? We also try to understand why certain types are in certain places and how climate change has already moved species around.”

For research to be effective, though, it needs to be done on a global scale because everywhere is different.

“On pictures seen from satellites,” explains Bowler, “you can see that in some areas of the globe, there is a lot of photosynthesis going on, for example, around the poles in the far north and the far south. This means that marine life is still very much active in these uniquely preserved environments.” What will happen, though, when these areas will be opened to oil drilling, extensive shipping and other polluting human activities? Perhaps they will become like the middle of the Atlantic or the Pacific oceans, where there is very little plankton activity left.

“For each of the myriad of different kinds of plankton, we can see how their abundance and their diversity change over the globe. We see that some places are diversity hotspots for some but not for others. What does it mean in terms of biodiversity? Is it not the case for other kinds of plankton, why not? Why is one type abundant in one place and not in another? What makes it that one can resist and another not in a specific location? All this has a meaning in terms of sucking the CO2 out of the atmosphere and in feeding the fish in our fisheries.”

Additionally, Bowler goes on, “the richer an ecosystem is in terms of biodiversity, the more robust and stable it is, because this means that if one species disappears, another takes its place. This is also important in terms of climate change because the more robust and the more stable an ecosystem is, the better it will be able to resist changes in temperature, acidification and pollution. If biodiversity is low, a change in temperature may cause extinction of some species and the crash of the entire ecosystem.”

Still think plankton is insignificant?

“The change we have created on Earth is so fast that we question whether the processes of evolution that make organisms adapt can keep up fast enough,” warns Bowler. “We are now burning in one year the equivalent of one million years’-worth of plankton deposits as fossil fuel, we are polluting the oceans with toxins and plastic, we are overfishing. … What we are doing is totally unnatural. No other creature has been able to influence the planet so much, our power is just massive. We are so powerful that we have become like a God. But things are getting out of hand and so the urgent challenge is that we have to start learning to act as a just and benevolent God.”