Associations and distribution of benthic nematodes in the Ethiopian Rift Valley lakes

The nematode associations in six Ethiopian rift lakes, one man-made lake, and three crater lakes were studied and related to water conductivity, lake depth and sediment particle size. The lakes investigated lie at moderate altitudes (1200–2000 m), are alkaline and vary in their conductivities. The rift lakes Abijata and Shala and the crater lakes Aranguadi, Kilotes and Chitu are soda lakes (K₂₅ > 6000 µS cm^?1), while the remaining five lakes and the man-made Lake Koka are within the freshwater range of conductivity (K₂₅ < 6000 µS cm^?1). A total of 16 species were identified including six new species. The nematode associations varied between lakes and were restricted to very few species in each lake. Most nematodes were restricted to non-saline lakes. The most dilute L. Zwai had a higher number of nematode species (12) and abundance than other lakes. The saline lakes Shala and Kilotes had nematode assemblages made up of only a single species (Mesodorylaimus macrospiculum). No nematodes were found in the hypersaline crater L. Chitu. Tobrilus africanus appeared more euryhaline than other nematodes occurring at conductivities as high as 15 000 µ S cm^?1 (L. Abijata). Five of the most common species (Dorylaimus sp., Monhystera stagnalis, Aphanolaimus tudoranceai, Tobrilus africanus and Actinolaimus perplexus) were associated with medium grained sand. A monthly variation in density of nematodes in L. Zwai is also shown.