Attached and planktonic algal communities in some inshore areas of Great Bear Lake

Abstract

The species composition and standing crop of epilithic, epipelic, and planktonic algae were determined in three widely separated inshore areas of Great Bear Lake during the summers of 1976, 1977, and 1978. The most frequently encountered diatoms in the epilithon were Tabellaria ftocculosa and Achnanthes minutissima regardless of location, whereas the predominant chlorophyte was Ulothrix zonata. These species were generally rare in the epipelon and were replaced in importance by Gyrosigma spenceri, Nitzschia obtusa, Cocconeis placentula, Amphora ovalis, and Achnanthes lanceolata, depending on sampling site. The densities of the epilithon and epipelon were low in June but increased gradually during the summer, reaching maxima of 78 × 107 and 120 × 107 μm3 cm−2, respectively (19.5 × 105 and 40 × 105 cells cm−2), in either August or September. These values are among the lowest recorded for fresh waters and are probably due to continually low water temperatures and wave action rather than nutrient limitation. The most important species in the plankton in all three sampling areas were Dinobryon bavaricum, Dinobryon sociale, Rhodomonas minuta, Cyclotella species, Synedra acus var. radians, and Ankistrodesmus falcatus. Plankton standing crops of up to 62 mg fresh weight m−3 were recorded in June at a temperature of 0 °C, and they increased to 70–91 mg m−3 (23.3 × 107−30.1 × 107 cells m−3) by September. These values are again among the lowest on record, a reflection of low water temperatures. The similarity in the species composition and standing crop of the plankton, epilithon, and epipelon in all collection areas was due to the similarity in water chemistry and temperature throughout Great Bear Lake.