Effects of Stream Permanence on Crayfish Community Structure

Abstract

Little is known regarding the impact of stream drying on community structure and habitat selection of lotic crayfish. Crayfish community structure was measured through quantitative sampling of riffle, run and pool habitats in 15 intermittent and 21 permanent streams in the Spring River watershed in the Ozark Plateau region of northern Arkansas and southern Missouri. MANOVA was used to determine whether stream permanence, habitat and crayfish size affect crayfish density and ANOVA was used to determine the effect of stream permanence and habitat type on species richness. Canonical Correspondence Analysis was used to determine the relationship between environmental variables and crayfish relative densities. Four crayfish species were collected: Orconectes marchandi, O. punctimanus, O. ozarkae and Cambarus hubbsi. Overall, crayfish densities were significantly greater in intermittent streams than in permanent streams with density of O. marchandi and O. punctimanus significantly greater in intermittent streams than in permanent streams. Densities of O. ozarkae and C. hubbsi did not differ significantly between the two stream types. Large individuals of O. punctimanus and O. ozarkae were found in significantly greater densities than small individuals. There was a significant relationship between crayfish relative density and abiotic environmental variables for permanent streams, but not for intermittent streams. In permanent streams, percent gravel, substrate diversity and mean current velocity were among the most important factors in determining crayfish density. Taxa mobility and predation risk are likely explanations for observed patterns of crayfish density.