Abundance and distribution of macroinvertebrates in relation to macrophyte communities in a prairie marsh, Swan Lake, Minnesota

We compared the macroinvertebrate communities among vegetation types in Swan Lake, a large prairie marsh in south-central Minnesota. Activity traps and sweep nets were used to sample macroinvertebrates during the summer months of 1992 and 1993. Twenty-four sites on the lake were sampled along six established transects. Each site was located in one of four different habitats, including three major macrophyte communities: Typha angustifolia, Scirpus acutus, Potamogeton spp., and an open water site having little or no vegetation. The diversity, relative abundance, and biomass of the invertebrates collected from each vegetation type were compared to assess which type of vegetation supported the greatest numbers and most diverse invertebrate fauna. A total of 16 orders, 46 families and 93 genera were identified. Results suggest that the open water sites produced the largest number of organisms, whereas the Typha sites produced the greatest total biomass of invertebrates. Nine orders showed significant differences in abundance among vegetation communities, but there were no significant differences in biomass of orders among vegetation types. There were significant differences in the mean diversities among vegetation community types. Typha sites supported the most diverse populations of macroinvertebrates and the open sites produced the least diverse populations. The abundance of six orders was significantly different between years and may be attributed to fluctuating water levels. Our results suggest that the occurrence and abundance of certain macrophyte communities may enhance the quality of a marsh for consumers of macroinvertebrates.