“If plankton disappears, many other species will disappear too”. In the second part of their interview, scientits Pierre Mollo and Pierre-Michel Forget, respectively specialists in plankton and in forestry, present their vision of the future, and especially the consequences of the disappearence of species.
In forests and in the oceans, biodiversity is being lost every day. Are there estimates concerning this loss of biodiversity?
Pierre Mollo: The rich variety of marine plants and animals, from the deep sea to birds, results from the diversity of plankton. Without it, whales can not live, and trying to protect them without worrying about the plankton would be like trying to save the orangutan without his forest. Plankton, an invisible forest, is both a lung for our planet and a breeding ground for our food. Observing planktonic organisms, just as we might observe birds, allows us to marvel at their extraordinary shapes, but also to monitor their health and to understand their vulnerability to multiple aggressions that threaten the delicate balance of marine ecosystems and plankton in particular. The challenge lies in the place where earth and sea meet – the receptacle of residues from land-based activities, the region where water quality is critical. Quality does not only mean the absence of pollution, but especially the presence of a wide diversity of phytoplankton and zooplankton. Today, it is urgent to focus our attention on the invisible, to see the ocean with new eyes and understand the abundance and vulnerability of its microscopic life.
Pierre-Michel Forget: Today people are talking about a “sixth extinction.” We are facing a massive disappearance of species in the tropical ecosystems that contain the bulk of biodiversity on earth. When we talk about the disappearance of 95% of a tropical forest, this means 95% of the species living within it are disappearing. A certain proportion of this biodiversity will persist in small areas of the forest, but the following question remains: will these areas be of sufficient size to allow species to persist? Will they provide enough resources for animals? Will they be sufficient for seed dispersal of plant species? It’s certain that adaptation will not be possible due to time constraints. Between 1970 and 2010, 50% of global biodiversity has disappeared or is in decline, mainly in tropical forests. When I travel across hundreds of kilometers in Malaysia, I see that the forest was simply wiped off the map and replaced with oil palms. I have trouble believing that biodiversity will be able to survive, and if it does, only in protected areas that still remain subject to strong anthropogenic pressures.
What will we lose with the disappearance of these species? What are the consequences of these extinctions?
Pierre Mollo: Managing living resources along coastlines means taking into account fishery resources in the open sea, ie, the biomass that lies off the coast. The earth nourishes the sea, thanks to rivers that are a real link. Living beings in the oceans need the food supplies of coastal marshes and estuaries to grow, just as the earth needs forests to feed its soil. Similarly, in the mud of estuaries, micro-organisms in the soil digest decaying plant material. These microorganisms in turn (via their excrement) feed bacteria which are transformed into nutrients essential to proper development of plants and algae.
The transfer of nutrients from these continental areas into the sea contribute to making coastal wetlands privileged sites, interfaces between land and sea. From this subtle mixture of mineral-rich fresh water and sea water will arise a diversified production of phytoplankton which in turn will nourish the whole marine food chain.
The wide diversity of marine plants and animals depends on the preservation of these natural balances. We will continue to live from the riches of the sea only if we protect living things on earth.
In fact, the entire biodiversity of the sea develops at the place where estuarine waters and deep ocean waters meet. The short lifespan of plankton makes it an excellent indicator of the quality of aquatic environments. It is the downstream synthesis of actions performed upstream. It is the result of human behavior and actions – physical, chemical, and biological; dams, pesticides, waste matter.
Modifications and disturbances of plankton contribute to the rarefaction of some species and can disrupt food webs and the pyramid of marine life. If one type of plankton disappears, many other species will disappear.
Pierre-Michel Forget: Take the example of tropical forests. If large species of animals that consume fruits and disperse seeds, such as elephants, tapirs, primates, bats, hornbills and toucans to name only the most emblematic ones, or if large carnivores that regulate these populations of frugivores and herbivores were to disappear, this means that the animals regulating the food chain disappear. And other animal and plant species begin to dominate, leading to cascading effects. Imagine the disappearance of primary consumer animals that have a key role in seed dispersal. Seeds would no longer be transported, they would accumulate at the base of trees and no longer serve to regenerate the forest. If you affect predators at the end of the food chain (‘top-predator’) – the large fruit-eaters – you harm the cycle of life that promotes a diverse and stratified forest. The frequency of large-seeded species (generally the biggest trees) decreases, and so the thickness of the canopy and its carbon storage potential decreases. Unstored carbon evaporates into CO2 and warms the planet. Decrease in the thickness of forest foliage results in fewer nutrients (insects, leaves, flowers, fruits, seeds, etc.) for the animals, the soil is depleted, the organic matter is less well recycled. The ground layers are thicker but not broken down, and at the time of leaching during the rainy season, all the leaves and non- recycled organic material will be carried by the rivers. This will increase the density of the water, making it less viable for phytoplankton, which ultimately will store less carbon and produce less oxygen. So the entire underwater food chain will be affected: zooplankton, invertebrates and other molluscs, fish and marine mammals, and at the end of the chain, us humans.
What is your message for future generations?
Pierre Mollo: The ocean, with its extraordinary force, covers 70% of the Earth’s surface, thus dominating our planet. In addition to its direct influence on the climate, it is the cradle of life. Its currents, gigantic or local, keep the water in constant movement, controlling the distribution of food and therefore of marine life. Currents make nutrients rise from the depths to the surface, thus providing food for the phytoplankton, the first link in the food chain without which the aquatic animal world would not exist.
The population of the world has its share of responsibility for the health of this vast and fragile ecosystem. Human activities represent the main threat to the inhabitants of the ocean. Like a game of dominoes where one falling piece can make all the others fall, when man causes an imbalance, provoking the loss of marine biodiversity, the consequences affect the entire game, including the player himself. Man’s influence on the ocean is equal to that of the ocean’s influence on man’s life and future. The solution is to respect the balance, starting with plankton.
Pierre-Michel Forget: Within the scientific community, we now consider that the present geological period (named the Anthropocene) is dominated by the human species. Since the human species evolved, we have significantly altered our habitat and almost the entire surface of the planet, to the point of leaving a geological signature, an indelible imprint in the ground for the next thousand or million years. There is debate about the beginning of this era, but it is certain that over the last hundreds of thousands of years, during the evolution of our species, CO2 levels in the atmosphere have never been higher. 2015 will forever be etched in memory as the year we passed the threshold of 400 ppm* (in February) – the logical continuation of 2014 as the hottest on record since 1880. But nature knows no timetable. Climatic events will continue inexorably, and become amplified.
Everything has been said. We have reached the limits of our extensive development, unfortunately not for the well-being of all the people of the world. We must act quickly, decelerate, ease off the accelerator and not rush headlong into the wall that rises before us, each year a little more difficult to avoid. I force myself not to be pessimistic – not always easy when studying tropical forests. It will be for future generations to repair the faults and mistakes of past generations and to ensure that this new era is not the shortest in the history of life on earth. There will not be another planet for our children, our grandchildren and their descendants.
Interview by Noëlie Pansiot
*ppm: parts per million