“The earth nourishes the sea”: a joint interview in 2 parts in view of the COP21 to be held in Paris from November 30 to December 11. Scientific experts Pierre Mollo and Pierre-Michel Forget explain the link uniting oceans and forests, the lungs of our planet, and how the two ecosystems interact. They emphasize the importance of integrating the ocean into the heart of climate negotiations.
A few months before the opening of the UN Conference on Climate Change in Paris, a group of research centers, institutions, and NGOs (including Tara) have launched the Ocean and Climate Platform. Supported by UNESCO, the initiative aims to put the ocean at the heart of the international climate debate. At the same time, our National Assembly has just adopted on first reading a biodiversity bill dedicated to “creating a new harmony between nature and humanity.” With its overseas territories and an extensive maritime area, France is among one of the most remarkable countries in terms of plant and animal biodiversity.
In this context and to go further, Tara interviewed two experts: Pierre Mollo, biologist specializing in the study of plankton, and Pierre-Michel Forget, Professor at the Natural History Museum and Project Manager in tropical ecology at the CNRS. In a question and answer session, the scientists explain what is happening from the heart of tropical forests to the middle of the ocean. From the highest peaks to the abyss, nature continues to render service to mankind.
What are the “services” provided by forests and oceans?
Pierre Mollo: Phytoplankton in the oceans produces a large amount of oxygen necessary for life in the water, through photosynthesis, but also through gas exchanges at the ocean surface. Phytoplankton provides two thirds of the planet’s oxygen; the other third comes from plants on land. Contrary to popular belief, the main producer of oxygen on Earth is not the forest, but phytoplankton that releases more oxygen to the atmosphere than all of the world’s forests combined, including that of the Amazon.
Phytoplankton is consumed by microscopic organisms (zooplankton) and small animals that are themselves food for bigger organisms, which are eaten in turn by other predators. Phytoplankton is at the base of the aquatic food chain. Micro-algae are not only appreciated by zooplankton, they are a preferred food for larger filter feeders such as oysters and mussels in their larval stage and throughout their adult lives. Mankind feeds on all steps of the pyramid including phytoplankton on the ground floor — spirulina, chlorella, etc.
Pierre-Michel Forget: Forests absorb water like a sponge, but also solar energy. This absorbed energy and the carbon fixed by the leaves during photosynthesis are stored in organic matter (carbohydrates), thereby limiting soil surface warming while reducing the concentration of carbon dioxide (CO2) in the atmosphere. So, forests protect us from a certain warming and increased carbon dioxide! Today a large proportion of tropical forest has disappeared: Nigeria and Vietnam are leading the way with the highest rate of deforestation, and have lost respectively 80% and 78% of their original forest cover between 1990 and 2005. Malaysia and Indonesia are now vying for first place for the highest deforestation rates in the world, particularly in Borneo, Sumatra and the Malay Peninsula. All these forests situated in the equatorial region were absorbing intense light and stocking CO2.
Is there a connection between these two ecosystems? How do they interact?
Pierre Mollo: At its base, phytoplankton creates organic matter from minerals that come from land via rivers. The earth nourishes the sea.
Pierre-Michel Forget: The 2 ecosystems interact a lot, there is ‘air flow.’ We forget to make the link between ocean warming and changes in precipitation on the continents. A forest like the Mata Atlantica (the Atlantic Rain Forest of Brazil) which continues to shrink, captures moisture from the ocean, stores it and re-distributes it to ecosystems. These two ecosystems are not sealed boxes, there are no oceans on one side and forests on the other. Organic matter stored in food chains, from plant to animal, decomposes in the soil and then is washed into storm water. And as all small streams make great rivers that flow into the oceans, forests will contribute to enriching organic matter, but also minerals in ocean waters. So there is also a ‘water flow’ from one ecosystem to another, conveying a wealth of dead organic material. Whole living organisms take advantage of this vector to move from one ocean to another, from one continent to another.
Pierre Mollo: The balance of nature depends on the diversity of species. Plankton, a common heritage of over 3.5 billion years, is the invisible but vital part. Its imbalance is often the result of human behavior and plays a warning role about the ill health of the planet.
Eutrophication has always existed. It is the process by which nutrients accumulate in a habitat (terrestrial and/or aquatic). It is caused by significant quantities of phosphorus and nitrogen in shallow waters and periods of strong sunshine. It is a natural phenomenon, self-regulating and without real danger in a balanced environment. Eutrophication has been accelerating for half a century and affected sectors have expanded. The increase is due to the intensification of human activities (wastewater discharge, diffusion of nitrogen fertilizers, etc.) and its consequences can pose a risk to public health. More than half of the world’s population currently lives on the coast where exchanges between land and sea take place. In this intensely concentrated area, excessive presence of some phytoplankton in coastal waters is problematic.
Interview by Noélie Pansiot