标题：Habitat of the Riverweed Darter, Etheostoma podostemone Jordan, and the Decline of Riverweed, Podostemum ceratophyllum , in the Tributaries of the Roanoke River, Virginia
摘要：When the riverweed darter, Etheostoma podostemone Jordan, was described in 1889, riverweed (Podostemum ceratophyllum) was abundant and the riverweed darter was closely associated with it. We compared current conditions of P. ceratophyllum beds to historical accounts, examined the association between the riverweed darter and P. ceratophyllum, determined substrate preferences exhibited by the riverweed darter during and after the spawning season, and compared habitat conditions in the North and South Forks of the Roanoke River. Podostemum ceratophyllum beds were rare in the South Fork of the Roanoke River and nonexistent in the upper North Fork. Causes for the decline of P. ceratophyllum are unknown, though sedimentation and reduced streambed stability are suspected. Median particle size was significantly lower in the North Fork compared to the South Fork. Riverweed darters were encountered in areas with a median particle size of 90mm, median depth-averaged velocity of 0.22m/s, and median depth of 24cm. Comparisons between microhabitat locations where riverweed darters were encountered and randomly chosen microhabitat locations revealed no significant differences; as a result, there is insufficient evidence to conclude that microhabitat selection by riverweed darters is non-random within shallow riffle habitats. However, spawning microhabitats of riverweed darters had higher velocities than randomly chosen microhabitats and higher velocities and depths than summer microhabitats.
