Burrowing and soil dependence in the invasive crayfish

The invasive calico crayfish Faxonius immunis digs burrows into banks and pond sediments. Burrowing behaviour is a crucial trait for the ecological success of crayfish because the burrow provides shelter and keeps humid conditions during dry periods; therefore it can be of aid for management purposes to understand under which conditions the species is not able to dig its burrows. In standardized lab experiments, adult F. immunis individuals were placed in a closed container containing water saturated sediment and left there for a simulated two-week drought period in three separate experiments. Survival rate, volume, shape, number of burrows and the ability to seal the entrance were noted and compared between different sediments, status of the major chelae and for the different sexes. F. immunis was able to survive the two-week experimental drought on all sediments. The survival rate was lowest for male crayfish on sand sediment. Results show that silt sediment allowed burrowing behaviour whereas the species was not able to dig a burrow in sand and gravel sediments. Female F. immunis had a higher tendency towards building cavern shaped burrows and had larger burrow volumes and seal diameters. A majority of dug burrows had a sealed entrance. As there were no burrows in sand or gravel, the management approach that uses habitat modification by gravelling sediments of invaded waters has a high potential to support the efforts in managing this invasive species in ponds.