Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, 1090 GT, Amsterdam, The Netherlands. E-mail: marijnissen@science.uva.nl

Endemic crabs and anthropogenic sedimentation in Lake Tanganyika, East Africa

Lake Tanganyika harbours freshwater crabs with a range of endemicity, from the highly derived family Platytelphusidae, that have evolved an intralacustrine species flock, to the endemic members of the widely distributed family Potamonidae, to fluvial non-endemic. The crabs are potentially critical links in the lake's food web. They are the largest invertebrates in Lake Tanganyika and they are common in most benthic habitats. The clear water habitats of the lake are currently under threat from anthropogenic sedimentation. We predict that the crab species in the lake will be affected by increased sediment deposition depending on their level of speciation.

The platytelphusids potentially radiated due to trophic partitioning. They have extremely derived feeding morphologies that may give them a competitive advantage in a stable environment where specialisation is favoured. The large claws of Platythelphusa armata for example, enable this species to crush the strong shells of Tanganyikan gastropods. Habitat alteration is likely to affect prey availability and predation success for carnivorous species. Other species of endemic crabs have less enlarged chelipeds and are morphologically inferred to be herbivores and detrivores. Sedimentation is likely to effect algal composition and thus foraging efficiency for herbivores. Similarly, the Platythelphusidae include a range of life history strategies, which are likely to be altered by increased sedimentation.

Despite their obvious importance, the crabs have previously been neglected in studies of Lake Tanganyika's ecosystems. We are initiating an integrative research program with ecological, evolutionary and conservation perspectives on the Tanganyikan crabs. As the highly endemic platytelphusids may be specialised to pristine habitats, they are likely to be threatened; nonetheless they are the best indicators of habitat health.