Relationships between vegetation cover (Schoenoplectus decipiens) and wetland macroinvertebrate assemblages in a semi-arid landscape (Eastern Cape Karoo, South Africa)

Abstract

This study investigated macroinvertebrate assemblage composition in relation to the cover of aquatic macrophytes (Schoenoplectus decipiens) for a set of 13 temporary depressional wetlands occurring within a semi-arid environment (Eastern Cape Karoo, South Africa). We hypothesised that invertebrate abundance and taxonomic richness would be higher in wetlands containing aquatic macrophytes than in those lacking them. It was expected that a positive relationship between vegetation cover categories (sparse, moderate and extensive) and invertebrate richness and abundance would be observed. In contrast to expectations, the macroinvertebrate assemblage was not significantly different across the three investigated categories. Non-parametric permutational MANOVA results indicated that the presence/absence of vegetation and wetland surface area had a significant effect on macroinvertebrate assemblage composition. Multivariate regressions (distance-based redundancy analysis) indicated that surface area, dissolved inorganic nitrogen and pelagic chlorophyll a concentration explained significant variation in macroinvertebrate assemblage composition in these wetlands. Overall, the presence or absence of vegetation appears to play a role in structuring the macroinvertebrate assemblages, but no convincing evidence was found for an effect of the vegetation cover gradient (sparse vs moderate vs extensive) on macroinvertebrate assemblages in these temporary wetlands.