Distribution and abundance of attached, littoral algae in 21 lakes and streams in the Northwest Territories

Abstract

Collections of epilithic, epipelic, epiphytic, and epipsammic algae were made from the littoral zone of 21 lakes and streams in the Northwest Territories during 1975 and 1976. Tabellaria flocculosa was the predominant species in the epilithon and epipelon, reaching maximum densities of 0.5–2.5 × 109 μm3/cm2 depending on watercourse. It was followed in importance by Achnanthes minutissima, Navicula spp., and Nitzschia frustulum, all of which occurred at densities of 0.1–0.3 × 109 μm3/cm2. While the only two common taxa in the epiphyton, A. minutissima and T. flocculosa, maintained populations of 1.0–1.3 × 109 μm3/cm2, the most frequently encountered epipsammic species, Amphora ovalis var. pediculus, Fragilaria construens var. venter, Achnanthes minutissima, and Achnanthes pinnata, reached maximum levels of 4 × 107 μm3/cm2. The growing season for the attached flora extended from June to October throughout the study area. All four communities displayed a unimodal growth curve during this period, reaching maximum abundance in either July or August. The end of the growing season came during the middle of October when the collection sites were frozen to the bottom.