2023-09-04 18:29:23
Water primrose, in the marshes of Vigueirat, in Mas-Thibert (Bouches-du-Rhône), in July 2022. NICOLAS FIGUERES/MARAIS DU VIGUEIRAT
At first sight, these golden yellow flowers that line the marsh, a vast expanse of motionless water where a few egrets hunt, only add to the charm of the place. But for David Grzyb, director of the Marais du Vigueirat, a nature reserve in the heart of the Camargue, they are rather “desperate”. “We intervened a year ago to tear everything out, and the water primrose has already recolonized half of the basin… It’s an endless fight to try to limit it”he says.
Originally from South America, this aquatic plant, introduced in France in the 19th century to adorn ponds and aquariums, was quick to escape into natural environments. It is now widespread in French wetlands, particularly in the Camargue, where it invades all the canals and marshes. Prohibited from import, sale and transport since 2007 at the national level, it has been included in the European list of invasive alien species since 2016. These biological invasions are considered to be one of the five main factors in the erosion of living things by the Intergovernmental Science and Policy Platform on Biodiversity and Ecosystem Services (Ipbes), the “IPCC of biodiversity”, which published on Monday 4 september, a major report on their impacts and monitoring.
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In the Marais du Vigueirat, water primrose, like baccharis, another invasive plant native to North America, appear as “the main threat to marshes and reedbeds”, Selon David Grzyb, for who “these species completely transform the environment and cause a net impoverishment of their biodiversity”. With its plant cover and dense root network, the water primrose quickly eliminates other aquatic plants, asphyxiates freshwater environments, and harms fish and the multitude of waterfowl that migrate or winter here. As for baccharis, it creates impenetrable thickets which supplant the reedbeds, habitat in decline on which many species depend for nesting or feeding: herons, including the very rare bittern, reed harriers, the European pond turtle ( a turtle), amphibians, aquatic snakes, dragonflies…
Uprooting of water primrose, in the marshes of Vigueirat, in Mas-Thibert (Bouches-du-Rhône), in July 2019.
Breeding, hunting and canals
Beyond the Marais du Vigueirat, the entire Camargue is affected by the worldwide phenomenon of biological invasions. The largest wetland in France, entirely artificial, is crossed by a network of canals which irrigate or drain the rice fields, meadows and marshes… also promoting the circulation of these species. “We are located downstream of the Rhône, and close to major ports, which are different entry points for invasive species”, explains Anthony Olivier, ecologist at La Tour du Valat, a Camargue research institute. Moreover, “by disturbing these natural environments, men have created new habitats, which favors the installation of these highly competitive species”, he adds. In 2005, the Camargue Regional Natural Park identified 39 invasive alien species threatening this territory, including seven animals and six plants. “already proliferating” : Louisiana crayfish, coypu, catfish, Florida turtle, pampas grass…
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