Microhabitat variations in diatom composition and stable isotope ratios of the epilithic algae in Lake Malawi

Microhabitat-level spatial variations in diatom and isotope compositions of epilithic periphyton in the littoral zones of Lake Malawi were examined using periphyton samples collected from seven regions of the lake. Discriminant analysis revealed a clear difference in diatom composition among the slopes of the rocks from which the samples were collected. This difference may be associated with interspecific variation in the adhesive power of diatoms. The slope of the rocks also strongly affected the stable carbon isotope ratios of periphyton, together with subsidiary effects of algae size class, sampling site, depth, and some of their interaction terms. The effect of slope can be explained by the decrease in photosynthetic activity along the slope, which originates from the decline in sunlight. Thus, the diatom composition and carbon isotope ratios may be good indicators of microhabitat and have the potential to be powerful tools for quantitative measurement of microhabitat utilization of epilithic algae-feeding consumers of this lake, including territorial cichlids.