The Influence of Depth, Rugosity, Food Quality and Primary Productivity on Abundances of Algivorous Fishes in Lake Tanganyika

Many tropical lakes have a diversity of fishes supported in part by algal productivity on rocks. We quantified densities and depth distribution of the two dominant algivorous cichlids at 10 rocky littoral sites in Lake Tanganyika, East Africa. We also measured rugosity, algal phosphorus (P) content, and primary productivity at each site. Fish densities were highest at 0.5 to 1m depth (1.5 fish m ^-2 ) and decreased exponentially with depth. Among sites, fish density and algal P-content were significantly correlated, but fish densities were only weakly correlated with rugosity and primary productivity. Algivores inhabit the shallowest water where primary productivity is highest, suggesting a strong effect of food availability on algivore distribution. However, the more modest among-site variation in periphyton productivity was not a good predictor of algivore densities, reflecting the complex interactions between resource availability and consumer density. The positive correlation between algal P-content and fish density may reflect spatial variation in P input, or be driven by fish excretion.