Although formerly common and widely distributed most of the unionid species are nowadays among the losers of anthropogenic changes of our environment. In Germany as well as in Baden-Württemberg the Thick river mussel (Unio crassus) – formerly the most common species with an impressively broad ecological spectrum – is currently threatened by extinction. Data on the current distribution of the different species and also on the genetic structure of the surviving populations is limited.
Despite various assessments specifically for the Thick river mussel, data on its distribution as well as on other unionid species are scattered and incomplete. In addition to a compilation of the existing records the project included localized mapping efforts across the area of the county.
For several species (e. g. Unio pictorum, U. crassus, Pseudanodonta complanata) it has long been discussed in literature to have subspecies or local races ("Danube-race", "Rhine-race") based on differences in shell morphology. Some authors interpret the distribution patterns of these forms even as hint to ancient connections of the drainage systems. For south-western Germany these considerations are so far entirely based on shell morphology. To approach these questions the project comprised a first pilot study exemplarily for the Thick river mussel applying population genetic methods (establishment of methods and assessment of results for selected populations).
The project was supported by the funds of the Fischereiabgabe and managed by the Regierungspräsidium Stuttgart.
Project lead: Dr. Ira Richling