Invasive species have led to changes in ecosystem structure, functions, and processes around the world. In aquatic systems, bivalves with their ability to lter feed can alter biogeochemical cycles and food web structures. The zebra mussel Dreissena polymorpha has got a lot of attention as it has caused large ecological and economical impacts in North America. Another less known but also very important freshwater invasive bivalve is the Asian clam Corbicula fluminea. This clam species has spread over North America in the last century and reached Europe in the 1980s. At the beginning of the 21st century, it was found isolated from other sightings at one spot in the eastern part of Lake Constance. From that point, it started to colonize the lake and has by now established itself well around the eastern end.
Daphnia spp. as the main zooplankton in Lake Constance is the basic food for planktivorous fish. Due to the regulations that reduced the pollution of the lake dramatically, fish stocks have declined in the last decades. Fishers have therefore asked to fertilize the lake with phosphate to increase the phytoplankton biomass and thus the one of the zooplankton. The goal of this thesis is to nd out how much the total ltering potential of C. fluminea in Lake Constance would be if it spread around the whole lake and see whether that would mean that the clam would prot from more phytoplankton instead of the Daphnia spp..
I estimated clam density at dierent depth levels at Lake Constance and calculated the ltered water volume using ltration rates from literature and a estimated potential area that the clams can colonize. I also looked at the depth distribution of the clams density and size and took sediment samples to correlate sediment properties with clam densities.
I estimated that the maximal mean ltration rate summed up over the whole lake is about 0.16 km³ per day. This equals about 5 times the mean discharge of the Upper Lake of Lake Constance. With this rate the clams would eectively lter the volume of the whole lake in roughly a year, the water volume above the thermocline in about 64 days. As this is much higher than the estimated potential of Daphnia spp. (at least 2000 times as much) it is possible that the Asian clam will lessen the food availability for the zooplankton in Lake Constance. However, more data and dynamics would need to be included to make a profound statement on what that means for the management of the planktivorous sh food web in Lake Constance.