Representation of aquatic invertebrate communities in subfossil death assemblages sampled along a salinity gradient of western Uganda crater lakes

We analysed subfossil death assemblages of aquatic invertebrate communities in a salinity series of 35 western Uganda maar-crater lakes to evaluate their potential as biological indicators of past habitat conditions in paleo-enviromnental research. The study region encompasses the climatological and hydrological gradient between the dry floor and moist shoulders of the Edward-George branch of the East African Rift Valley, and includes mesotrophic to hyper-eutrophic, and shallow unstratified to deep meromictic lakes with a surface-water salinity range between 101 and 135 400 mu S/cm. Focusing on non-chironomid aquatic invertebrates with good fossil preservation, we found that fossil larval remains of the Dipteran families Culicidae, Ephydridae, and Stratiomyidae are good indicators of saline environments. Our data further suggest that the abundances of Bryozoan statoblasts and Chaoboridae are indicative of, respectively, the fraction of the littoral zone covered by aquatic macrophytes and of lake trophic state, but a lake reference data set more specifically designed to cover variation in these environmental factors will be needed to determine the strength of these relationships. In these small, simple lake basins, recent death assemblages recovered from a single mid-lake surface-sediment sample provides a more complete inventory of local aquatic invertebrate communities and the distribution of species among lakes than exploratory live sampling of those taxa in a selection of littoral, benthic and pelagic habitats.