Lake Constance, one of the largest Alpine lakes on the border between Germany, Austria and Switzerland, has undergone major changes over the past century. From the 1950s to the 1980s, Lake Constance experienced a period of severe eutrophication, resulting in significantly elevated nutrient levels. Although the natural trophic state of the lake has been restored, irreversible changes in the aquatic communities have occurred. In addition to eutrophication, climate change and in particular the invasion of non-native plant and animal species are threatening natural biodiversity. This leads to changes in food webs and affects the functioning of the ecosystem in Lake Constance. In particular, the three-spined stickleback (Gasterosteus aculeatus) and the quagga mussel (Dreissena bugensis) are causing major problems. Stickleback and quagga mussel populations have exploded in recent years, with sticklebacks becoming the most abundant pelagic fish species. Quaggas can settle in all water depths, causing problems with intake pipes and other structures. Quaggas are also an important competitor for zooplankton, which feed on phytoplankton. We hypothesise that these two invasive species are responsible for the decline in fish yields and fisheries in Lake Constance. We present a large EU-funded project (www.seewandel.org) that investigates the causes and consequences of such invasions for Lake Constance. We present the latest results on these invasive species and their consequences for the lake.

Authors:

Piet Spaak, Eawag, Aquatic Ecology  (spaak@eawag.ch)

Josephine Alexander, Eawag, Dept. of Aquatic Ecology  (josephine.alexander@eawag.ch)