Mesocosm Experiments reveal the ecological impact of invasive mussels on waterfleas in Peri-Alpine Lakes
Peri-alpine lakes are a beautiful part of our natural heritage from glacial times. However, these gems are consistently threatened by a multitude of factors caused by anthropogenic influences and are facing new and unprecedented challenges with ongoing global change. Invasive species, rising water temperatures due to climate change and high nutrient inputs are only a few of the factors that have negative effects on our lake ecosystems.
A major invader of peri-alpine lakes in recent years have been the Quagga mussels. These filter feeders originate from the Black and Caspian Sea region and have managed to spread to our lakes through shipping trade. They have expanded very quickly throughout peri-alpine lakes, reaching densities of up to 4000 mussels/m2 in Lake Constance (Bodensee) (Kleine Zeitung, 2025).
Since they filter out massive amounts of algae, these mussels disturb nutrient cycles in lake ecosystem and are in direct competition for food with many zooplankton species. Declining numbers of zooplankton then in turn influence fish stocks that feed on them. A substantial part of the zooplankton in peri-alpine lakes is made of waterfleas (Daphnia species). These small Crustacean are an important part of the lake ecosystem since they exert a major grazing pressure on algae and are a food source for fish. However, they are in direct competition with the Quagga mussels for algae.
To estimate the influence of invasive mussels on waterflea communities in our ecosystems, we are doing mesocosm experiments to determine how the waterflea species composition might change with rising mussel densities in our lakes. Mesocosms are basically 300L barrels in which natural conditions can be mimicked and manipulated to understand the influence of changes on ecosystems better.
For these experiments, we will use three Daphnia species that are dominant throughout peri-alpine lakes to represent the Daphnia community. Before our main experiment can take place, pilot experiments are carried out to test the experimental setup and treatment conditions that we want to test. In the first pilot experiment, nutrients were added in different concentrations to stimulate algal blooms to test the optimal supplementation in later pilots. The second pilot experiment, currently under way, tests the influence of quagga mussels on the Daphnia community with varying mussel densities. 12 mesocosms are being used for the second pilot experiment, each inoculated with an integrative plankton sample from lake Mondsee to mimic the lake’s plankton communities, mussels in different densities and an experimental Daphnia community consisting of the three species. Already, after 3 days of inoculation with the mussels and Daphnia, the experiment shows big differences in the visual algae concentration.
In the summer of 2026, the main experiment will take place based on the insights collected during the current pilot experiments. In this main experiment, 40 mesocosms will be used to investigate how quagga mussels affect the Daphnia species composition in the peri-alpine lakes.
The further spread of the invasive mussels will likely cause a huge filtration effect in our peri-alpine lakes, causing a reduction in phyto- and zooplankton densities and likely also a reduction of fish. However, the more we know about these effects on our ecosystems, the better we can work on methods to mitigate the change and deal with the consequences. And that is exactly what we are working on in this project.
Alina Aigner, BSc.
Bibliography
Kleine Zeitung. (2025, Juli 07). From Kleine Zeitung:
https://www.kleinezeitung.at/international/19877866/quagga-muscheln-werden-im-bodensee-zum-problem