The Abundance, Distribution and Diversity of Benthic Invertebrates of Lake Malombe

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 macroinvertebrates
which were identified to the lowest taxa and enumerated to estimate abundance for the
lake. The biomass of macro-fauna is being reported here for the first time and coincides with a decline
in fish catches on Lake Malombe. 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 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 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 overfishing,
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.