No bigger than 4 centimeters, a greedy mollusk is threatening the biodiversity of Alpine lakes. The quagga mussel has recently been lining the bottom of several of the lakes. On August 17, traces of DNA from the invertebrate, native to the Dnipro basin in Ukraine, were detected in Lake Annecy, in the French Alps. "It's not surprising, since we're located near several contaminated lakes," said Isabelle Domaizon, director of the Observatoire des Lacs, a specialized research laboratory. Additional analyses were carried out on data from the summer of 2022: Traces of quagga were already perceptible at that time, according to the researcher.
Like many invasive alien species – responsible for half of the world's species extinctions – this freshwater mussel risks altering the ecological balance of the lakes it is colonizing. With concentrations of up to 5,000 individuals per square meter, this mollusk filters 2 liters of water per day, taking nutrients from other species. "In American lakes, where the quagga has been present for over 30 years, water clarity has risen from 2 meters to more than 15, with nutrients being dragged down," said Benjamin Kraemer, a researcher at the University of Konstanz in Germany)and author of a study on the subject.
In 2015, the mussel appeared in Lake Geneva. The following year, it was spotted in Lake Constance, on the border between Switzerland, Germany and Austria. Observed in 2019 in the Lac du Bourget, its presence is also attested in the lakes of Serre-Ponçon and Annecy.
Quagga mussels find Alpine lakes a favorable ecosystem for their development. "There are the right temperatures, favorable depths and the chemical properties of the water suit them perfectly," said Kraemer. "In most cases, they even out-compete populations of zebra mussels, another invasive species," said Piet Spaak, a researcher at the Swiss Federal Institute of Aquatic Science and Technology.
No one yet knows whether these mussels originate directly from Ukraine or the United States, which has long been overrun. Either way, they have traveled with ships, clinging to their hulls or in the ballast water for the larvae. And, once they have settled in, the situation is unlikely to be reversed: "If you find one, it's already too late; we can't remove them all," continued Spaak.
"In Serre-Ponçon, quaggas pose a medium-term threat to two endemic species of anodont mussels, as they cling to them and hinder their movement," said Damien Combrisson, project manager at the Ecrins National Park. "All species can be indirectly threatened, as quaggas have an impact on the entire food chain by removing phytoplankton," said Nicole Gallina, secretary general of the International Commission for the Protection of the Waters of Lake Geneva.
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