Aquatic Angiosperms at Unusual Depths in Shoal Lake, Manitoba-Ontario

Abstract

Shoal Lake (elevation 323 m) was found to contain extensive macrophyte communities growing at depths of 12-14 m and consisting of the angiosperms Elodea canadensis, Najas flexilis, Potamogeton foliosus, P. zosteriformis, Myriophyllum exalbescens, Ceratophyllum demersum, Megalodonta beckii, Zosterella dubia, Lemna trisulca and the aquatic moss Drepanocladus sp. Aside from one previous record for E. canadensis at higher altitude, the above angiosperm species have not been reported at such depths before. These communities were observed throughout two consecutive growing seasons. Plants at these depths received an estimated 0.5-1 % of surface light. Besides light, other factors which may have allowed for the existence of these communities were warm summer temperatures in deep water and the presence of oxygen in the sediments during most of the ice-free season.