Distribution and habitat diversity of subterranean amphipods in the Rocky Mountains of Colorado, U.S.A.

Abstract

Subterranean amphipods have been collected from 35 locations on the eastern and western slopes of the Continental Divide in Colorado. All belong to the exclusively subterranean genus Sty-gobromus. Five species have been identified, two of which are undescribed. Specimens have been collected from (a) the hyporheic zone of rivers, (b) interrupted streams, (c) springs, and (d) seeps at elevations from 1597-2134 m a.s.l. Stygobromus occurs in several habitat types in interrupted drainage basins including sources, seeps, and isolated pools containing leaf detritus. All habitats contained waters which were cool to cold with dissolved oxygen values ranging from 4.3 ppm to fully saturated. Most waters exhibited soft or medium hardness, although pne spring containing an undescribed species of Stygobromus had very hard waters (203 ppm bound CO 2) and was mildly saline (913 mg/l TDS). There is evidence that the subterranean amphipods are phreatobites which, only under special conditions, establish relatively permanent populations in epigean habitats. Although little is known regarding ecology, zoogeography, or even taxonomy of the subterranean fauna of this region, stygobromid amphipods from the Cordilleran of western North America are apparently represented by fewer well differentiated species per unit area than their congeners from the geologically older Appalachian region of eastern North America where nUjIlerous species are found in caves .