Habitat use and selection within Ozark lotic crayfish assemblages: Spatial and temporal variation

Habitat selection by small (<= 15.0 mm carapace length (CL) and large (> 15.0 mm CL) individuals of the crayfish, Orconectes marchandi, O. ozarkae, O. punctimanus, and Cambarus hubbsi was examined at 4 sites in 2 streams in the Spring River watershed. Replicate quadrat samples were collected from riffle, run, pool, emergent vegetation, stream margin, and backwater habitats during the summers of 1998 and 1999. A 3-factor ANOVA was used to determine effects of habitat, species, and year on crayfish density for each site and stream. Habitat selection by crayfish was determined by comparing habitat used to habitat available for each species and size class. There were significant temporal differences in habitat used by some species-size classes of crayfish, but significant species by habitat interactions were detected at all sites for both crayfish size classes. Small 0. ozarkae and 0. punctimanus used mainly vegetated habitat, whereas both size classes of C. hubbsi used mainly riffles and runs. Large individuals of Orconectes spp. and small 0. marchandi were more broadly distributed across pools, backwaters, stream margins, and vegetated habitats. Selection indices showed that individuals of all small Orconectes species and large O. ozarkae and O. punctimanus strongly selected vegetated, backwater and stream margin habitats at all sites and times on both streams, even though these habitat types comprised only similar to 15% of the available habitat. Both size classes of C. hubbsi selected mainly riffle habitats. Redundancy analyses showed a significant positive relationship between crayfish densities and percent emergent vegetation and a negative relationship with current velocity and depth. Backwater, stream margin, and vegetated habitats can contain extremely high densities of crayfish and may act as important habitats, especially for Orconectes species.