Habitat specialization and sensitivity to change in a threatened crayfish occupying upland streams

1. Crayfish are culturally and ecologically important species in freshwater ecosystems, but many are now threatened with extinction, due to threats such as habitat loss. Depending on their habitat selectivity and sensitivity, freshwater crayfish could provide effective targets for stream monitoring, restoration and conservation. This study used repeated field surveys of the threatened Murray crayfish, Euastacus armatus (family Parastacidae), to establish their habitat preferences and sensitivity to habitat loss across mesohabitat and microhabitat scales within upland streams of south‐east Australia. 2. Selectivity analysis revealed that upland populations of E. armatus displayed a strong preference for areas of intermediate water flow velocity, deeper water, and stream beds dominated by boulders and gravel. Variations in E. armatus density among and within the two upland streams aligned with these microhabitat preferences, with best‐subsets analyses revealing that E. armatus abundance hotspots were best predicted by models combining water depth with percentage cover of boulders, gravel and overhanging riparian vegetation. 3. Major shifts in stream habitat condition from 2009 to 2015 (e.g. 32% and 50% decline in boulder and overhanging vegetation cover, respectively) was associated with a 91% decline in E. armatus mean density within glide‐pool mesohabitats. 4. These findings highlight how habitat specialization in threatened crayfish such as E. armatus may render them sensitive to changes in stream habitat condition, and how targeted monitoring, restoration and conservation of their preferred habitats could yield multiple benefits for montane freshwater ecosystems. Copyright © 2016 John Wiley & Sons, Ltd.