Marmorkrebs are parthogenetic crayfish in the genus Procambarus. Their provenance is unknown, but they were discovered in hobbyists' aquaria in Germany in the mid 1990s, and have since been introduced into the North American pet trade. Marmorkrebs are a potential invasive pest species. For example, they have already been introduced into Madagascar, where they may threaten endemic crayfish species. We are trying to estimate the risk, and possible consequences, of any accidental introduction of Marmorkrebs into North American waters. First, we conducted an online survey of hobbyists who keep Marmorkrebs as pets to estimate how widely, and how long, Marmorkrebs have been in distributed in the North American pet trade. Second, we are testing whether Marmorkrebs can successfully compete with other crayfish species during aggressive interactions. Anecdotal information suggests that Marmorkrebs are less aggressive than other crayfish. If Marmorkrebs consistently lose fights with crayfish of other species, this could affect their ability to compete for resources, which might in turn limit the spread of Marmorkrebs through natural ecosystems. To test this, Marmorkrebs and red swamp crayfish (Procambarus clarkii) were isolated for three weeks to place all individuals on an equal social status. A Marmorkrebs was paired in a small tank with either a conspecific or P. clarkii of similar size and their behavior was recorded for 30 minutes or until a clear victor emerged.
Marmorkrebs are being kept as pets in at least thirteen American states and one Canadian province across North America, with the earliest report dating to 2005. These survey results suggest that an accidental introduction could occur almost anywhere in North America. Preliminary results from aggressive interactions indicate that Marmorkrebs can win fights against similarly sized P. clarkii. Intraspecific interactions were slower to begin and less intense than interspecific interactions. The ability to compete successfully with other species indicate that competition would be unlikely to limit the spread or impact of Marmorkrebs if they were released into North American waters. This, combined with the reproductive potential of a parthenogenetic crayfish where a single isolated individual can reproduce, indicate the threat posed by Marmorkrebs in North America is not trivial.