SPATIAL-DISTRIBUTION OF FRESH-WATER MUSSELS - THE ROLE OF HOST FISH AND METABOLIC-RATE

1. Three species of the superfamily Unionacea live in Bavarian trout streams: the freshwater pearl mussel Margaritifera margaritifera which usually occurs alone, and the unionids Unio crassus and Anodonta piscinalis which are frequently associated. 2. We found no evidence for competition between M. margaritifera and the unionids. Two types of habitat factors were analysed: (i) the occurrence of host fish, which does not explain the distributional relationships of mussels; and (ii) hydrochemical factors indicating a lower productivity in the rivers inhabited by M. margaritifera. 3. With respect to physiological differences, M. margaritifera is separated from the other two species by low growth constants and low metabolic rates. We conclude, therefore, that the metabolic rate is an important factor governing distribution of the species: M. margaritifera is able to grow in rivers with low food availability, whereas the higher metabolic rates of U. crassus and A. piscinalis presumably necessitate a richer food supply.