Risk assessment of a mysterious invader: Marbled crayfish in Japan

Background/Question/Methods

Understanding where non-indigenous species might become established usually means understanding the native ecology of a species. Thus, newly discovered species are particularly difficult to assess, because so little is known of their basic biology. An example of a species that has gone from being unknown to science to a potentially invasive species on several continents in less than a decade is Marmorkrebs. Marmorkrebs are a lineage of parthenogenetic marbled crayfish that were discovered in the European pet trade. They are closely related to the slough crayfish, Procambarus fallax, which live in the southeastern U.S. There are no known naturally occurring populations of Marmorkrebs, but due to human introductions, they have been found in natural habitats overseas, and established populations in at least two countries (Madagascar and Germany). One Marmorkrebs has been found in Japan, where it could pose both ecological and agricultural problems if it became established. First, Japan has only one endemic crayfish species, Cambaroides japonicus. This species is endangered and could suffer further from competition with an exotic crayfish. Second, rice is a staple crop in Japan. In Madagascar, Marmorkrebs thrive in rice paddies and eat the plants. To determine if Marmorkrebs pose a threat to Japanese ecosystems, we modeled the potential distribution of Marmorkrebs in Japan using MaxEnt. We created five models, using “native” populations (using P. fallax as a proxy for Marmorkrebs), introduced populations, and combinations of the two to train the models.

Results/Conclusions

All the models predicted that some regions of Japan were suitable habitat for Marmorkrebs: large regions of the islands of Shikoku, Kyushu, and some parts of eastern Honshu. Marmorkrebs appears to pose little threat to the native C. japonicus, which lives on the island of Hokkaido and northern Honshu. The models predicted that Hokkaido was unlikely habitat for Marmorkrebs.  Marmorkrebs could pose a more substantial threat to rice production, however, because models showed several regions with highly suitable habitat for Marmorkrebs had high rice production.