Conservation Genetics and Ecology of European Freshwater Pearl Mussels (Margaritifera margaritifera L.)

Despite the fact that mollusc species play important roles in many aquatic ecosystems, often little is known about their ecology, biodiversity and population genetics. Freshwater pearl mussels (Margaritifera margaritifera L.) are among the most critically endangered freshwater invertebrates, facing serious population declines and local extinctions. The goal of this study is to contribute knowledge for designing conservation strategies for the species by combining conservation genetics and ecological investigations. Altogether 14 polymorphic microsatellite markers were developed for M. margaritifera, representing the first published microsatellite markers for an European freshwater bivalve mollusc (order Unionoida). The markers revealed wide ranges of allelic richness and heterozygosity levels and proved to be suitable for monitoring of neutral genetic divergence and diversity in order to describe the current genetic structure of pearl mussel populations. The genetic diversity and differentiation of the last and most important central European pearl mussel populations from the drainages of Elbe, Danube, Rhine, Maas and Weser were assessed in order to determine conservation units (CUs), to select priority populations for conservation, and to deduce conservation strategies on a genetic basis for free-living populations and for supportive breeding measures. A high degree of fragmented population structure and different levels of genetic diversity within populations were detected. This observation can most likely be explained by historic, demographic and anthropogenic effects. The methodology of non-destructive sampling with no impact on living populations was established for pearl mussel DNA-analyses (dead individuals and haemolymph sampling). In addition, the successful use of shell-DNA was demonstrated. The potential of using mollusc shells for DNA-based analyses and the required precautions and limitations to avoid erroneous results were discussed. This study also explored the potential of separating annual growth increments of pearl mussel shell carbonate layers, and their suitability as long-term archives for up to 100 years. Stable isotope investigations of inner nacreous and outer prismatic shell carbonate increments demonstrate that pearl mussel d 13 C shell carbonate signatures record individual metabolic signals extending over several years and that a high percentage of respiratory CO 2 (community and mussel respiration) contributed to shell aragonite formation. In combination with d 15 N signatures of mussel tissues and potential food sources, these analyses allowed an assessment of the trophic level and of the origin of the mussel diet. The study on the status of host fish populations and the fish species richness in European pearl mussel populations characterised typical fish communities in pearl mussel streams and reveals that a lack of host fish only seems to be limiting for pearl mussel reproduction in specific areas. Intact and functional pearl mussel populations were found to occur under extremely oligotrophic conditions with lower host fish densities and biomasses than disturbed central European populations without juvenile recruitment. The effects of stocking measures with glochidia infected host fish as a conservation strategy were discussed. Due to the pearl mussels´ wide geographical distribution, their complex life cycle and extraordinary reproductive strategy, the global phenomenon of serious decline can have different and multiple reasons in different regions. Conservation strategies in general and those for freshwater pearl mussels in particular can greatly benefit from a holistic and combined approach of integrating conservation genetics and ecological studies to retain a maximum of the species´ biodiversity and evolutionary potential on the one hand, and try to identify their habitat requirements and restore their habitat to meet the specific requirements during all stages of the life cycle on the other hand. Thus, conservation strategies for pearl mussels can be key examples for the development of conservation strategies for other aquatic organisms and the ecosystem functioning upon which they depend. Generally, conservation efforts should move away from single species and pattern protection towards process and persistence conservation for ecosystems.