The contribution of riffles and riverine wetlands to benthic macroinvertebrate biodiversity

Benthic macroinvertebrates collected in biomonitoring programs are a potentially valuable source of biodiversity information for conservation planning in river ecosystems. Biomonitoring samples often focus on riffles; however, we have only partially assessed the extent to which riffle biodiversity patterns reflect those of other river habitats, particularly riverine wetlands. Using a standard biomonitoring protocol, we assessed the richness, composition and magnitude of variation of macroinvertebrate assemblages in riffles across 18 sites in the Nashwaak river catchment, and compared these to samples from adjacent riverine wetlands. Despite containing on average fewer taxa per site than riffles, riverine wetlands demonstrated similar levels of taxon richness at the catchment scale. There was strong assemblage separation between habitat types, and riverine wetlands displayed significantly greater assemblage variation than riffles. Riffles and riverine wetlands did not demonstrate significant correlations in terms of taxon richness or assemblage variation, though this may be partially due to the scale at which we collected observations. Principal component analysis with vector fitting suggested that (log) sub-catchment area was an important factor structuring riffle assemblages, while depth was potentially important for riverine wetland assemblages. We discuss the implications of these results for the use of biomonitoring data in systematic conservation planning, and identify future research that will improve our understanding of the role riverine wetlands play in maintaining catchment biodiversity and ecosystem processes.