Distribution and Ecology of Amphipoda (Crustacea) in Colorado

Abstract

Hyalella azteca is common and distributed in a wide variety of standing waters and springs of plains and mountains between 1050-3400 m in Colorado [USA]. Gammarus lacustris is uncommon and generally restricted to mountain ponds and lakes between 2500 and 3400 m where water temperatures do not exceed 20.degree. C. Hyalella was found at 148 stations and Gammarus at 29 stations. Both species are characteristic of littoral areas containing rooted macrophytes and coarse bottom debris; such waters are anaerobic or frozen to the bottom in winter. No significant habitat differences were found with respect to pH, water color, total dissolved solids and minimal dissolved O2 concentrations. Hyalella occurred over a greater range of water hardness, but in laboratory aquaria both species had similar survivorship curves in hard waters. The thermal death point for Gammarus was 26-28.degree. C; for Hyalella it was 35-37.degree. C. Crangonyx gracilis and Hyalella azteca inermis were each collected at single localities in Colorado.