EPILITHIC ALGAL COMMUNITIES OF THE BUJUKU-MUBUKU RIVER SYSTEM, RWENZORI MOUNTAINS, UGANDA

The epilithic algal flora, consisting predominantly of diatoms, is des cribed from a major river system of the Rwenzori Mountains, Uganda. Tw enty seven samples were taken between altitudes of 900-4510 m and almo st all were dominated by the diatom Achnanthes minutissima var. affini s. A total of 43 diatom species was recorded and an ordination using d etrended correspondence analysis showed that the community composition was related to altitude. Species diversity was low, and negatively co rrelated with altitude. The low diversity in the upper regions can be related to physical instability caused by steep gradients in the river systems, resulting in cascades and high turbulence. Green algae and c yanobacteria also occurred including the rarely recorded Desmonema wra ngelii. All of the waters were of low ionic strength, oligotrophic and circumneutral. Minor differences were found in the water composition of the Mubuku and Bujuku river systems but they did not correlate with diatom distribution.