Distribution and Microhabitat Dynamics of the Threatened Bayou Darter, Etheostoma rubrum
The bayou darter, Etheostoma rubrum, is endemic to the Bayou Pierre system, southwest Mississippi. In the Bayou Pierre system, E. rubrum occurred in mid-reach, typically third to fourth order, stream sections. Microhabitats of E. rubrum were in swift (xBAR = 79 cm/sec), shallow water, with firm, coarse substrata (xBAR particle size = 16-32 mm). In a laboratory stream, E. rubrum chose a larger substratum (pebbles, 32-64 mm). Etheostoma rubrum were consistent in microhabitat characteristics throughout the year but became increasingly associated with large cover (eg., logs, cobble, and boulders) during the winter. Laboratory experiments demonstrated that under cold-water, higher flow (33.5 cm/sec) conditions, E. rubrum actively used large objects as refugia, even when provided a pebble substratum. Current refugia are probably an important habitat component for winter survival of E. rubrum, especially during periods of high stream flow.