Phytoplankton in Lake Tanganyika: a Comparison of Community Composition and Biomass off Kigoma with Previous Studies 27 Years Ago

The composition and temporal distribution of phytoplankton was studied in the northern basin of Lake Tanganyika and was compared with existing data from 1975 from a nearby locality. Sampling was conducted every 2 weeks from February 2002 to February 2004 at a pelagic station in Lake Tanganyika off Kigoma (Tanzania). Changes in algal community structure were observed: the reported cyanobacteria-chrysophytes-chlorophytes community of 1975 was replaced by a cyanobacteria-chlorophytes-diatom community. Moreover differences in species composition were detected between 1975 and 2002-2003. Besides the rarity of chrysophytes not all the species reported from 1975 were observed and conversely new taxa were found. While taxonomic issues make a direct comparison difficult, our data provide evidence for real floristic changes. These changes may be related to the decreasing productivity of the lake, as was recently reported for Lake Tanganyika and confirmed in the present study.