Influence of an invasive crayfish species on diurnal habitat use and selection by a native crayfish species in an Ozark stream

The crayfish Orconectes neglectus chaenodactylus has recently been introduced into the Spring River drainage in southern Missouri and northern Arkansas and appears to be displacing the native species O. eupunctus. To determine if O. eupunctus and O. neglectus chaenodactylus compete for habitat, we examined if either species shift habitat's when in the presence of one another. Habitat use of juvenile and adult crayfish was determined in six habitat types (backwater, pool, riffle, run, stream margin and vegetation) with a quadrat sampler during July/August 2003 at three sites: (1) an upstream site where O. neglectus chaenodactylus occurs, (2) a zone of overlap where both species occur and (3) a downstream site where O. eupunclus occurs. Habitat selection was determined by comparing habitat use to habitat availability. Redundancy Analyses were used to determine the relationship between crayfish densities and measured environmental variables (current velocity, water depth and percent boulder, cobble, pebble and sand). Orconectes eupunctus showed no shift in habitat use, habitat selection and species-environmental relationships between the downstream site and the zone of overlap. However, O. neglectus chaenodactylus did show a shift in habitat use and habitat selection between the upstream site and the zone of overlap, although no shift in species environmental relationships was found. Competition for habitat between O. eupunctus and O. neglectus chaenodactylus did not appear to cause the habitat shift by O. neglectus chaenodactylus since O. neglectus chaenodactylus shifted into habitat's used and selected by O. eupunctus. This study suggests that O. eupunclus and O. neglectus chaenodactylus may not compete for habitat. It is possible that habitat is not limiting in this system or that competition is taking place, but at a microhabitat level. Further study is needed to examine other potential mechanisms causing the displacement of O. eupunctus.