Todd, J. 1, E. Michel2, D. Cleary2, I. Kingma2, A. Cohen3

1Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, U.K. E-mail: jont@nhm.ac.uk
2Institute for Biodiversity & Ecosystem Dynamics, University of Amsterdam, 1090-GT Amsterdam, The Netherlands
3Dept. of Geosciences, University of Arizona, Tucson AZ 85721 USA

Point endemicity confounds diversity and impact assessment for gastropod species flocks in Lake Tanganyika

The endemic thiarid gastropods of Lake Tanganyika are famous for their morphological diversity, convergence on marine forms, and species richness. Lavigeria is demonstrably the most diverse "species flock" forming clad in this ancient rift lake, with high levels of sympatry among approximately 30 species recognised to date. These grazing herbivores are the dominant benthic macroinvertebrates in the rocky littoral zone. While some species are widely distributed along most of the 1400 km of shoreline, others are point endemics with distributions measured in kilometres or hundreds of meters. We have sampled both regionally (lake-wide) and locally to catalogue molluscan diversity, determine community composition, and test for habitat disruption. Snails are impacted by increased anthropogenic sediment accumulations on rocky substrates. Although we expect that much of the point endemism be primary (local speciation), subfossils indicate that current point endemic L. coronata was previously found at sites now impacted. We found that previous estimates of the malacofauna seriously underestimate overall diversity through limited geographic sampling. Moreover, species replacement even on the scale of a few kilometres makes controlled comparisons difficult for testing the effects of sediment impacts on the endemic fauna. Despite this we can show sedimentation correlates with decreased diversity on both regional and local scales.