We describe a new occurrence of parthenogenetic Marmorkrebs in southwestern Germany and give a synopsis of recent records of this species in Europe. Including the most recent records, 15 Marmorkrebs records are currently known, most of which are from Germany. At least six records represent established populations, which is an alarming increase beyond the one Marmorkrebs population known prior to 2010. Most established populations occur in lentic habitats near conurbations, typically in highly frequented secondary habitats, such as gravel pit lakes. In three instances, Marmorkrebs migrated over land, demonstrating their potential for active spread, and two invasive populations endanger indigenous crayfish populations. Most Marmorkrebs populations are large and are most likely several years old, suggesting a considerable lag between introduction and detection. Marmorkrebs populations in Europe are most likely the result of deliberate releases from aquaria, although secondary introductions may have occurred in one instance. Because Marmorkrebs are still widespread in the European pet trade, which most likely generates substantial propagule pressure, it is likely that the number of established populations will further increase over time. To mitigate the risk of further harmful crayfish releases, we suggest the prohibition of trading live high-risk crayfish species, including Marmorkrebs.
Keywords: aquarium introductions • marbled crayfish • invasiveness