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

Abstract

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 (K,, > 6000 PS cm-*), while the remaining five lakes and the man-made Lake Koka are within the freshwater range of conductivity (K,, < 6000 PS cm -').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 aficanus appeared more euryhaline than other nematodes occurring at conductivities as high as 15 000 PS cm -' (L. Abijata). Five of the most common species (Dolylaimus 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.

Relation between nematode communities and trophic state in southern Swedish lakes

“…In addition to the bottom-up effect observed in this study, previous findings suggest a positive top-down effect by predators on nematode diversity, as demonstrated by in a study of 13 alpine lakes. Beyond these two relationships, many factors, especially intra-and interspecific competition, resource availability, and sediment characteristics, drive the structure of nematode populations (Tudorancea & Zullini, 1989;Strayer et al, 1997;Eyualem et al, 2001;Michiels & Traunspurger, 2005c). Only a few species (4-5%) out of the 157 species identified were common between lakes and many species occurred only in a single lake.…”

Nematode communities of small farmland ponds

“…Since a mud layer was present in all studied ponds, mud was likely not demonstrably important to explain density and diversity variations among the individual ponds. The availability of oxygen, though its effect on nematode may be less than other meiofauna, is most probable another important factor negatively influencing nematode density and diversity (e.g., Prejs, 1977;Tudorancea & Zullini, 1989;Eyualem et al, 2001;Vidaković & Bogut, 2004). Oxygen concentrations could not be safely included in our statistical analysis.…”

Aquatic nematodes from Ethiopia I

“…Twelve bottom samples yielded two species of nematodes that are the only reported to date from Lake Abiyata, Brevitobrilus graciloides von Daday, 1910 as Tobrilus africanus Zullini, 1988, andMesodorylaimus macrospiculum Zullini, 1988 (Tudorancea & Zullini, 1989) .…”

“…plicatilis, Hexarthra jenkinae, Lacinularia elliptica (Green & Seyoum, 1991) . Tudorancea & Zullini (1989) from 11 bottom samples reported only a single species, Mesodorylaimus macrospiculum Zullini, 1988 . Tudorancea & Zullini (1989) from 11 bottom samples reported only a single species, Mesodorylaimus macrospiculum Zullini, 1988 .…”