What’s next?
But how did the little troublemaker from the Black Sea region get into German waters in the first place? It is assumed that it stowed away in the ballast water of cargo ships in Germany, where it was first detected in 2005 and finally landed in Lake Constance via the Rhine. “This probably happened due to the overland transport of sports boats,” explains Franz Schöll from the Federal Institute for Hydrology, “the quagga mussel can survive on the ship out of the water for a while.”
Apart from the ecological consequences, the explosive development of the mollusk in Lake Constance means increased maintenance and high economic costs. Because it not only grows on ships, leisure boats and fishing nets, but can also get into the treatment plants and pipes of the water supply via its larvae and grow there, which causes an enormous cleaning effort.
© Sarah Nagele (detail)
Stefan Riebel fishing in Lake Constance | For the professional fisherman, the mussels are more than just a nuisance. They change the entire ecosystem and thus make life difficult for edible fish. Sometimes he has the feeling that he is pulling the last whitefish out of the lake, he says.
“The spread of the quagga mussel on Lake Constance can no longer be stopped,” says Petra Teiber-Sießegger with certainty. The SeeWandel project is committed to ensuring that bodies of water that have not yet been affected are protected as best as possible from the immigration of invasive species. “People have to be made aware of the issue,” she explains. It would be advisable to regularly clean all boats, but also surfboards, air mattresses or stand-up paddle boards. Sometimes the biologist goes for a walk on the bank and tries to explain the problem to the people, but the topic is difficult to convey.
“One quickly overlooks the fact that we humans have changed our habitats so much that they are no longer resilient and that invasive species only appear in the first place,” Hahn points out. For example, people like to talk about the endangerment of native large mussels by the quagga mussel, “but the maintenance of waterways, construction activities, the clearing of rivers and canals endanger large mussels much more”. In Germany, almost all bodies of water have changed significantly and are far removed from natural conditions. “We have to think about which waterways we want to keep navigable in the future,” he says. By renaturing waterways one could contribute to the stabilization of ecosystems.
Schöll sees the situation rather pragmatically. Although he also advocates raising public awareness and taking measures, he also relies on natural regulation by ecosystems. Don’t forget that these are always changing. “You have to observe the processes over a much longer period of time,” he adds: “The zebra mussel, for example, has been in the Rhine for almost 200 years. Is it a newcomer to the river or isn’t it already one of the native organisms?” Once neozoa are there, it’s virtually impossible to get rid of them. At best, the spread can be minimized.