The community composition, distribution, and nutrient status of epilithic periphyton at five rocky littoral zone sites in Lake Malawi, Africa

The epilithic periphyton of Lake Malawi is dominated by heterocystous cyanoprokaryotes (blue-green algae/cyanophytes) and diatoms containing endosymbionts capable of nitrogen fixation, though in some locations impacts such as sediment and nutrient loading have shifted the algal community structure towards dominance by diatoms and chlorophytes. Overall, diazotrophic (capable of N-2 fixation) Calothrix spp. dominated the littoral periphyton communities at almost all sites/depths located within this study. The biovolume of associated heterocysts tended to decline with depth and was similar between sites. Diazotrophic endosymbionts within Rhopalodia spp. were a common feature of the algal community at all sites/depths, although they have not previously been reported in the literature for Lake Malawi. While the use of stoichiometric C:N:P ratios to determine the nutrient status of naturally-occurring periphyton communities was confounded by detrital and non-living portions of the algal matrix, the dominance of diazotrophic algae suggests that the rocky littoral zones are N-limited systems.