A Rapid Assessment of Macroinvertebrates Associated with Salvinia molesta In Moremi Game Reserve, Okavango Delta

Abstract

Salvinia molesta is an invasive species in the Okavango Delta. The plant forms monotypic covers in places where it occurs and thus affects macroinvertebrates diversity within them. Three habitats with low, moderate and heavy infestation by the weed were selected inside Moremi Game Reserve to study macroinvertebrates diversity within them. A total of 31 taxa were identified in the study area, with the highest number occurring in heavily infested habitat. An analysis of variance (ANOVA) indicated that the means for the number of individuals collected at each habitat were significantly different from each other. And the result from calculations of Shannon Wiener diversity index showed that heavy infestation by S. molesta is associated with high macroinvertebrates diversity. There were also more functional feeding groups (FFGs) in sites that were heavily infested by the weed. However, highest numbers of macroinvertebrates associated with low oxygen environments, particularly Hirudinae, occurred in places with heavy infestation by the weed. This was not surprising since S. molesta depletes oxygen from the water bodies as was indicated by the results on dissolved oxygen (DO) measurements from the study area. Therefore, S. molesta infestation in the Okavango Delta should be totally controlled to ensure a high DO environment typical of a freshwater wetland ecosystem, which would also result in a shift in the diversity of macroinvertebrates in the area.

Keywords: Salvinia molesta, macroinvertebrates, invasive, functional feeding groups, Okavango Delta

Tropical Freshwater Biology Vol. 17 (1) 2008: pp. 13-23