The inshore benthic macroinvertebrates of Lake Nabugabo, Uganda: seasonal and spatial patterns

Abstract

Lake Nabugabo, Uganda, is a lake of particular interest because of the unusual nature of its benthic macroinvertebrate community. In this study we quantified the spatial and temporal distribution of benthic macroinvertebrates within the lake with a focus on habitat associations in inshore areas. We focused on four inshore habitats: Nymphaea lotus/Nymphaea caerulea (water lily), Miscanthidium violaceum, Vossia cuspidata (hippo grass) and forest edge. The most notable characteristic of the Nabugabo fauna was the absence of bivalves and crustaceans and the scarcity of gastropods that made up only 1.8 % of the numerical abundance of the benthos. The numerically dominant taxa were ephemeropterans (77.7 %) and dipterans (11.1 %). Annelids (5.4 %), odonates (2.8 %) and trichopterans (1.3 %) comprised a much smaller component of the benthic assemblage. Total invertebrate abundance and the abundance of major taxa did not vary significantly across months, but habitat effects were evident. The water-lily habitat was very depauperate, which may reflect the low levels of dissolved oxygen near the sediments in this habitat. Lake Nabugabo is extremely poor in salts, mean conductivity in inshore sites ranging from 22.3 to 26.4 μS/cm and 22.6 to 37.9 μS/cm (K25) for surface and bottom waters,  respectively. The low conductivity (low concentrations of ions) in Lake Nabugabo may limit colonization by molluscs and crustaceans that, with their calcareous shells or exoskeletons, may require water with a higher mineral content.

Key words: aquatic invertebrates, East Africa, Ephemeroptera, macrophytes.