Attached Algae on Artificial and Natural Substrates in Lake Winnipeg, Manitoba

Abstract

The attached algal assemblage on navigational buoys and natural rock substrate in Lake Winnipeg in 1969–70 was examined, in the fall after 145 days growth, as part of an overall limnological survey of this important Canadian Great Lake. Only three phyla were represented: Cyanophyta, Chlorophyta, and Chrysophyta (Bacillariophyceae). Green and blue-green algae were more abundant in the south basin, and diatoms were more common in the more oligotrophic north basin. Ulothrix zonata occurred only on substrates in the north basin, and Cladophora cf. callicoma was found only in the south basin. On both natural and artificial substrates a distinct zonation pattern related to water transparency or available light was prevalent. Preliminary results indicated that light was the most important physical factor affecting growth and specific composition of attached algae on substrates in Lake Winnipeg. Biomass values from all stations (dry weight) ranged from 1.7 to 29.1 mg/cm2; with the greatest values consistently occurring between 10 and 25 cm deep on buoys in the south basin. Diatom density and diatom volume were estimated from buoy samples and varied respectively, within the range 2.00 × 105–6.65 × 106 diatoms/cm2 and 0.32–10.00 mm3/cm2. Though direct evidence is lacking, it appears that nutrients may limit growth of attached algae in the north basin, whereas in the south basin, light is the major limiting factor. The specific composition of the algal assemblages on particular buoys was more related to the physical–chemical features of a major river plume in close proximity to the buoy than to a homogeneous Lake Winnipeg water mass. This factor, together with greater turbidity in the shallower south basin, is largely responsible for the observed heterogeneity among the attached algal assemblages in Lake Winnipeg.