Abstract

The benthic zone of Lake Malombe was sampled for invertebrates, fungi and bacteria using an Ekman Grab measuring 15.2 cm by 15.2 cm. Thirty-six stations were surveyed for macro-invertebrates which were identified to the lowest taxa and enumerated to estimate abundance for the lake. Snails were the most dominant macro fauna, belonging to four genera Melanoides, Bellamya, Bulinus and Lanistes with the mean densities of 177.5, 34.7, and 4.3 and 0.1 m-2 individuals, respectively. Blood worms and Tubifex were also present. Although there are few such studies in Malawi, it was generally postulated that dominance of snails is a recent phenomenon following previous studies which showed that the invasion of a form of Melanoides of Asian origin; its success might be responsible for its proliferation. The benthic substrate was mainly composed of mud, clay granules, sand and bedrock. The biomass of macro-fauna is being reported here for the first time and coincides with a decline in fish catches on Lake Malombe. The prevalence of Melanoides species and other high pollution tolerance species suggests that there is high ecosystem modification due to anthropogenic activities including sediment and nutrient loading from agricultural practices in the surrounding area. Compared to Lake Malawi and Upper Shire, Lake Malombe is by far the most productive. There were significantly higher (P<0.5) densities of aerobic, anaerobic bacteria and fungi, demonstrating the importance of the detrital food chain. Therefore, future programs aimed at enhancing fish restoration in Lake Malombe would be advised to include a suite of bottom feeding fish species. The state of benthos found in Lake Malombe is an indication of confounding impacts of over-fishing, climate change and catchment-wide activities. Thus, use of QIIME software could unravel microbiome characteristics, including climate change signatures. Similarly, further studies on food webs could contribute to a better understanding of the Lake Malombe trophic functions.

Key words: Benthic invertebrates, aquatic snails, fungi, bacteria, ecosystems, food chain, Lake Malombe.