BENTHIC ALGAE OF SOUTHERN BAFFIN ISLAND. III. EPILITHIC AND EPIPHYTIC COMMUNITIES1

Blue-green algae–mainly Aphanocapsa pulchra (Kz.) Rabh., Oscillatoria tenuis Ag., Schizothrix muelleri Naeg., and Lyngbyn spp.—were predominant, in the epilithic communities of Baffin Island rivers and lakes during 1972, usually accounting for more than 90% by numbers and volume of the total flora. Diatoms were only important early in the growing season (June) with Achnanthes marginulata Grun., A. kriegeri Krasske, and Tabellaria flocculosa (Roth) Kz. being most common. Standing crop in one river increased from near 0 in June to 6.0 × 10⁴ cells/cm² (2.2 × 10⁸μ³/cm²) in July and back to near 0 again by October. Low levels of nitrate nitrogen probably limited algal numbers, while flooding, light, and grazing by herbivores appeared to have little effect. Changes in algal standing crop in the lakes followed much the same pattern as outlined above. However, the maximum amount of algae was considerably greater than that recorded from the rivers, reflecting the greater availability of nutrients. Lyngbya nana Tild. was the main algal species attached, to filaments of Mougeotia sp., reaching greatest development (5.0 × 10⁴ filaments/cm²) during September. On the other hand, diatoms–mainly Ceratoneis arcus Kz. and varieties, Fragilaria spp., and Synedra spp.–were predominant in the community floating among the filaments with maximum standing crop (64.48 × 10⁶ cells/g dry weight of Mougeotia) occurring in July. The small diameter of the Mougeotia filaments was probably the main factor limiting the size of both the attached and free-floating communities.