GILBERT, D.*; MCINTYRE, P.B.; MICHEL, E.; MULONGAIBALU, M.; SAPP, J.; Massachusetts Institute of Technology, Cambridge; Cornell University, Ithaca, NY; University of Amsterdam, Netherlands; University of Kisangani, Democratic Republic of Congo; University of California, Berkeley: Responses of herbivorous cichlid fishes to anthropogenic sedimentation in Lake Tanganyika

Anthropogenic sedimentation poses a serious threat to littoral communities in the East African rift lakes. Herbivorous fishes may be particularly susceptible due to reduced accessibility and quality of food resources. We studied the effects of sedimentation on two algivorous cichlids, Tropheus brichardi and Petrochromis polyodon, at sediment-disturbed and reference sites along the northeastern shore of Lake Tanganyika. T. brichardi uses fused oral combs to graze filamentous algae, whereas P. polyodon gleans unicellular algae using mobile pads of brush-like teeth. Our results show that sedimented sites have a higher proportion of inorganic matter and less total algae than reference sites, confirming that food quantity and quality are decreased. T. brichardi are more aggressive at sedimented sites, suggesting that decreased food quality increases the importance of defending feeding territories. The territoriality of P. polyodon does not appear to be influenced by sedimentation, though their grazing frequency is significantly reduced. The added bulk of inorganic sediments at disturbed sides may have a saiting effect. In contrast to these behavioral shifts, population densities, gut length, and body condition of T. brichardi and P. polyodon are similar at disturbed and reference sites. This suggests that behavioral plasticity alleviates the effects of sedimentation on these algivorous fishes.