Spatial variability of aquatic macroinvertebrate assemblages in the Okavango Delta, Botswana: considerations for developing a rapid bioassessment tool

Abstract

Spatial variability in macroinvertebrate assemblages of the Okavango Delta, Botswana, was examined to evaluate differences in assemblages at a regional and habitat scale. Sampling was undertaken six times during a one-year cycle from 2005 to 2006, with 228 macroinvertebrates samples collected from different aquatic habitats in 22 sites in four study areas. Sixty-four taxa, mainly families, and >30 000 individuals were recorded. Multivariate analysis of aquatic macroinvertebrates revealed that the distribution of macroinvertebrate fauna is relatively homogenous among study regions, with some variation in number of taxa. Differences were observed in the macroinvertebrate assemblages associated with different aquatic habitats, with fauna from deltaic habitats (floating vegetation, inundated floodplain and marginal vegetation) different from non-deltaic habitats (isolated, seasonally flooded pools and isolated, temporary, rain-filled pools). Within the deltaic habitats, there were no significant differences among the habitats in terms of number of taxa and abundance, although assemblages and frequency of occurrence of taxa differed among habitats, providing evidence of habitat preferences for certain taxa. Future development of a macroinvertebrate-based bioassessment tool should account for aquatic habitat, although the tool does not need to be region specific. Temporal variability of macroinvertebrate assemblages should be examined to evaluate potential hydrological effects on the tool.