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Abstract:
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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 by snorkeling along transect line 5m wide from 0-8m depth, at 10 rocky littoral sites in lake Tanganyika, East Africa. We measured rugosity, algal phosphorus (P) content, and primary productivity at each site. Fish densities were highest at 0.5 to 3m depth (1.5 fish/m2) and decreased exponentially with depth within sites. Among sites, fish density and algal P-content were significantly correlated, but fish densities were only weakly correlated with among sites variation in rugosity and primary productivity. At all sites, 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. Similarly, the positive correlation between algal P-content and fish density may reflect spatial variation in P input or be driven by fish excretion. |
