UTILIZATION OF COARSE WOODY DEBRIS BY EPHEMEROPTERA IN 3 OZARK STREAMS OF ARKANSAS

Collections of ephemeropteran nymphs were made from both coarse woody debris (CWD) and benthic habitats from the White River, Illinois River , and Clear Creek of northwestern Arkansas, from February 1991 through February 1992. Two-way analysis of variance comparing the density of mayflies between habitat types, and among seasons yielded significant main effects only with habitat type. There was no two-way interaction. Mayflies were significantly more abundant in benthic habitats than on CWD. Of at least 35 species of mayflies, 11 were collected in signifi cantly greater densities from benthic habitats, and only two from CWD. Degree of decay was an important factor in determining the abundance of species on CWD. Species with a preference were more abundant either on wood with loose bark remaining, or well decayed wood containing ma ny interstitial spaces. The volume of biofilm on CWD was a factor in d etermining the abundance of only one species.