Habitat type and seasonal effects on the distribution and density of plecoptera in Ozark streams, Arkansas

Plecoptera nymphs were collected from coarse woody debris (CWD) and benthic habitats from the White River, Illinois River, and Clear Creek of Northwest Arkansas from February 1991 through February 1992. Two-way analysis of variance comparing habitat type and season showed significant main effects. Densities were significantly greater in benthic habitats than on CWD and greater during winter and spring than during summer and fall. Significant two-way interactions were found between habitat type and season. Multiple regression analysis revealed a significant relationship among the seasonal density of winter stoneflies and flow rate, water temperature, and dissolved oxygen; densities increased as water temperature decreased and as dissolved oxygen concentration and flow rate increased. Densities of stonefly species with slow univoltine, semivoltine, or fast univoltine spring and summer life cycles showed no significant relationship with these factors. Two-way analysis of variance indicated that most species inhabiting coarse woody debris are found on wood with loose bark or wood that is well decayed and has many interstitial spaces. Prostoia completa (Walker) was the only species whose abundance was influenced by the volume of biofilm present on CWD and increased biofilm volume led to increased density. These results suggest that benthic habitats are preferred by most species of Plecoptera, but that CWD may also be an important habitat type for some species.