Great Basin Naturalist


Benthic macroinvertebrates were collected during the ice-free season (1 July–20 October) over a five-year period from a chain of alpine lakes and intervening streams in the Green Lakes Valley (3,347–3,615 m) in Boulder County, Colorado. A list of taxa was developed for 1981 and 1982, with taxonomic additions for 1983–1985 and comments on community structure, seasonal and elevational changes in species abundance, and noteworthy occurrences. A total of 111 taxa was collected, of which 84% occurred in streams, 58% being exclusively lotic. Dipterans composed 73–81% of total abundance in streams. The littoral benthic zone of lakes was predominantly trichopterans and dipterans, 44–60% and 24–39%, respectively. Numerically important organisms in various lakes and streams were chironomids, simuliids (particularly Metacnephia), oligochaetes, and the bivalve Pisidium casertanum. An isolated lake and its outlet stream, with unique characteristics, were the sole locations of Gammarus lacustris (Amphipoda) and Glossiphonia complanata (Hirudinea). Manipulated lowering of a lake along the main drainage exposed abundant and luxuriant colonies of the bryozoan Fredericella sultana. This organism was found on 43% of all rocks sampled, a preponderance heretofore unknown for this, or any, ectoproct in alpine or arctic lakes.