Silent invasion: Sinanodonta woodiana successfully reproduces and possibly endangers native mussels in the north of its invasive range in Europe

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AbstractThe explosive global spread of Sinadonta woodiana, a large‐bodied unionid mussel of East Asian origin, potentially affects the functioning of freshwater habitats and threatens native mussels. Molecular data indicate that its invasion in Europe started with a single colonization event, followed by in situ adaptation. This study traces one of the possible routes of such adaptation. It documents a population of S. woodiana with a known history of a two‐stage introduction: first, from a heated water source to a production fish pond in northern Poland, and subsequently from that pond to the study site. As the latest local transfer occurred more than 15 years before the study, the abundance of young S. woodiana in various age classes provides proof of ongoing in situ reproduction and resolves the question of the ability of S. woodiana to permanently colonize thermally unpolluted water bodies in areas with prolonged and cold winters. The study also shows that translocations of glochidia‐infested fish and/or adult mussels between water bodies in such areas result in the establishment of new self‐recruiting populations. Together, these findings show that further expansion of S. woodiana into colder regions and establishment of new populations in already invaded areas are to be expected. The relative abundance of S. woodiana and the native unionids: Anodonta anatina and A. cygnea was 40%, 18%, and 42%, respectively. S. woodiana contributed to 65% of the total mussel biomass. Individuals in the first three size classes, corresponding to the 2‐ to 4 year age classes, composed 50% of S. woodiana, 37% of A. anatina, and 26% of A. cygnea. The high proportion of young individuals in S. woodiana indicates population trajectories toward a gradually increasing dominance of this species and possibly reflects its negative impacts via interactions with host fish and competition for resources.