It is an unusual sight. An aluminum schooner sailing off the mouth of the Congo; on the deck, men throwing nets in which they never bring fish, other men handling strange instruments connected to computers… After long weeks of navigation at sea, the oceanographic research sailboat Tara ventures currently off Angola and the DRC.
The objective of the scientists on board is simple, even if its implementation remains complex: to measure plastic pollution from several African rivers and their impact on the ocean. After the Orange River, in South Africa, and before Gambia and Senegal, it is Congo’s turn to undergo its medical examination. Even if he is a little reluctant: Tara was to go up the river to Matadi and take a series of samples in its course – we are talking about plastics and microorganisms – but the Congolese authorities have placed the amount of the authorizations to be able to sail on the Congo. A somewhat high sum for a few pollution samples…
Environment: from Cape Town to Dakar, the schooner Tara takes the pulse of the South Atlantic
“The Tara schooner will not go up the Congo River as initially envisaged, having not obtained the necessary guarantees for navigation on the river, and the hoped-for research permit, indicates Romain Troublé, director of the Tara Océan foundation. We adapt accordingly and will dedicate eight days of research on the plume of the river from the mouth to the open sea, outside the exclusive economic zone of the Democratic Republic of Congo. This study will make it possible to document the massive contribution of this river to the South Atlantic, like the work carried out on the Amazon in 2021.”
Study the different pollutants
A marine biologist attached to the CNRS (France), Douglas Couet is responsible for training scientists in mission protocols Microbiomes, launched nearly two years ago by the Tara Ocean Foundation. It thus ensures the continuity of the practices, determined upstream by the researchers within the framework of the AntlantECO program of the European Union. Between each stopover, the schooner’s journey is divided into “stations” during which scientists take multiple samples. “We planned to make five stations per river, explains Douglas Couet. One at sea, one in the estuary, one downstream from a town, one upstream from the same town, and a final one as far upstream as possible to, if possible, reach zero salinity. We will study the different pollutants, in particular plastics, but not only. »
Since the end of April, Tara teams have been working off the African coast to study this area of the South Atlantic that is little known to scientists. Among their objectives, sieve and magnify two major upwelling areas – off Namibia and Senegal – and four river areas. To achieve this, the scientists on board have not a magnifying glass and a sieve but various precision instruments bearing more or less poetic names. Thus, the “regent” and the “manta” are very fine-mesh nets allowing the collection, either in depth for the first or on the surface for the second, of the microorganisms that make up the plankton as well as the infamous microplastics.
The “rosette” is a little jewel of technology allowing water to be recovered, with a system of remote-controlled bottles, at different depths (up to more than 1000 meters). The interest? Know what the different layers of the water column contain according to the penetration of light, the degree of salinity, the oxygen level, the temperature, the amount of chlorophyll, etc. So many measurements provided by another instrument, the CTD (Conductivity-Temperature-Density), a sort of giant thermometer plunged vertically up to several thousand meters below the surface.
Wealth of sea water
Once back on deck, the samples taken undergo different operations depending on the studies carried out by the scientists: most are filtered, some are preserved by adding chemicals (borax, formalin) or immersed in liquid nitrogen. Every three months, the samples are sent to the Génoscope in Évry (France), which forwards them to various specialized laboratories for analyzes that can take two or three years. In the end, the amount of data obtained is very vast: DNA of microorganisms, nutrients, trace metals… “We have 30 protocols on board, explains Douglas Couet, which allow us both to determine the genetic and morphological diversity of the plankton and to characterize the physico-chemical environment in which it lives: seawater.
Like the authorities of certain countries, this sea water can sometimes be recalcitrant. Salty, it corrodes metals. Indomitable, aggressive, it puts equipment to the test. Especially on a 36 meter schooner which hardly has any free space. Thus, between Walvis Bay (Namibia) and Luanda (Angola), the connected cable allowing the famous “rosette” to be lowered into the depths has given up the ghost, attacked by rust. It took all the ingenuity of Guillaume Bourdin, an oceanographic engineer attached to the University of Maine (United States) to cobble together a backup system.
Every breath is a gift from phytoplankton
“There’s always something going on on board, I’m not shocked,” says Thulani Makhalanyane, a South African microbiologist on board between Cape Town and Pointe-Noire (Congo). When ce It’s not the material that yields, it’s a person who is sick. There are always variables that we cannot control. The main thing is to know how to adapt. Be that as it may, all the samples we take on the African coast can be used and valued because for the time being, we have very little data on the ocean in this region of the world. A philosophy shared by Douglas Couet. “We generally always manage to adapt to the vagaries,” he says. You have to be happy with what you did, rather than thinking about what you didn’t do. The environment is demanding, of course, but we will be able to learn some interesting lessons. These waters are poorly known. »
Impact on the entire food chain
Knowing how the oceans work better, spending money to study plankton might seem secondary. However, our life directly depends on it. “Each breath is a gift from phytoplankton, writes Christian Sardet in his book Plankton, the origins of life (Ulmer editions). Photosynthetic bacteria and plant protists produce as much oxygen as all forests and land plants. And for three billion years, plant plankton has been absorbing huge quantities of carbon dioxide, regulating, through the carbon cycle, the temperature, the climate, as well as the productivity and acidity of the oceans. In other words, protecting dolphins, whales and sperm whales is good, but protecting coccolithophores, radiolarians, foraminifera or chaetognaths is better!
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In 2019, the Tara Foundation set up a mission specially dedicated to the study of micro and nano-plastics which led it to take samples from several European rivers: the Elbe, the Rhine, the Seine, the Loire, the Garonne, the Ebro, the Rhône, the Tiber. While the presence of these pollutants in the oceans has been well known for years, it was then a question of understanding the sources and mechanisms of their dispersion. Coming mostly from land, plastic particles can persist for more than a thousand years in the marine environment and have an impact on the entire food chain. They come directly from our daily consumption: synthetic clothing fibers, various packaging, etc.
Three years after this European study, Tara is now tackling an unknown territory: the bed of African rivers. Failing to go to Matadi and to take samples planned around Boma, the scientists will study the plume of Congo waters in the Atlantic. For safety reasons, the crew will avoid the Niger delta, only approaching the coast to go up the Gambia and Senegal rivers.
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The fight can only be won on land, those who campaign against our irrational use of plastic products are used to saying. Hence the educational work, knowledge sharing and skills transfer implemented by the Tara Ocean Foundation in the various countries visited. During each stopover – Cape Town, Walvis Bay, Pointe-Noire, Banjul, Dakar – the schooner welcomes new African researchers on board, who can share their knowledge and benefit from those of scientists who are more experienced in the protocols used.
Stopovers are also an opportunity for the crew as a whole to meet the local scientific community, groups of students, decision-makers, with the aim of raising their awareness of the cause of the oceans. On deck, enthusiastic children from Walvis Bay, Luanda or Pointe-Noire listen attentively to the explanations of sailors and scientists. It remains to be seen which decision makers ils will become.