Effects of landscape disturbance on animal communities in Lake Tanganyika,East Africa

Watershed deforestation, road building, and other anthropogenic activities result in sediment inundation of lacustrine habitats. In Lake Tanganyika, t his threatens the survival of many rock-dwelling species by altering the st ructure and quality of rocky habitats. We investigated the relationship bet ween habitat quality, as related to watershed disturbance intensity, and th e biodiversity of faunal communities at three rocky littoral sites of low, moderate, and high disturbance. Turbidity measurements and other environmen tal observations confirmed that our lake sites represented a gradient of di sturbance conditions. We documented difference sin species density (number of species per constant area or time), species richness, abundance, and tro phic ecology for fishes, molluscs, and ostracods. Fish censuses were perfor med by scuba divers at 1-20 m and by remotely operated vehicle (ROV) at 40- 80 m. In the fish surveys, abundance, species density and richness, and her bivory reached their maxima at intermediate water depths. The depth range o f herbivores, however, was restricted at higher-disturbance sites. The ROV fish surveys at the high-disturbance site showed high species richness desp ite low species density and abundance, and piscivores were proportionally m ore prevalent than in all other surveys. Molluscs censused by diver quadrat s and sieve samples showed decreasing species richness and species density (sieve samples only) with increasing disturbance and no significant abundan ce trend. Ostracod species richness was similar between low- and moderate-d isturbance sites but was markedly lower at the high-disturbance site (speci es density and abundance data were not available). Our faunal analyses sugg est that all three taxonomic groups are negatively affected by sediment inu ndation but may have varying response thresholds to disturbance. Further, t his study emphasized the utility of using complementary survey techniques t o monitor and ultimately manage biodiversity in complex freshwater ecosyste ms.