Extensive reed stands are characteristic for the shallow, wind-sheltered littoral zones in many European lakes. Although reed constitutes an important physically complex habitat for benthic macroinvertebrates, spatial variability in taxonomic composition and diversity of benthic macroinvertebrates in reed stands has been rarely studied. We analyzed the spatial distribution, taxonomic composition and diversity of macroinvertebrates of reed stands in relation to lake morphometry, geographical location, morphological, physico-chemical and substrate characteristics. The three studied lakes Ostrowiec, Plociczno and Sitno were located in the Drawa National Park in Western Poland. We analyzed a dataset consisting of 27 dipnet samples (1 m2sampled area each), i.e. three reed transects per lake and three sampling points in each transect (shore, center and lakewards edge). The effects of environmental variables on macroinvertebrate communities were analyzed by NMDS, environmental fit and ANOSIM using Bray-Curtis distance matrices (R: package vegan), indicator species analyses and Spearman-Rank Correlations using % taxonomic group densities, taxa numbers and diversity metrics.
Water depth gradually increased from the shore to the lakewards edge of the studied reed stands. Especially shore sites were characterized by a high degree of physical complexity, i.e. high amounts of coarse organic matter (COM; e.g. leaves, twigs) and coarse woody debris (CWD). The macroinvertebrate community composition in all three studied lakes was strongly correlated with oxygen concentrations and pH: Communities at shore sites with a low oxygen concentration/pH were distinctly different from center/lakewards sites with a high oxygen concentration/pH. Several Macroinvertebrate metrics, e.g. the % Coleoptera and Margalefdiversity, were negatively correlated with oxygen concentration and pH, i.e. had higher values at physically complex shore sites with high amounts of COM and CWD and low oxygen concentrations. An indicator species analysis revealed Tinodes waeneri, Orthotrichia sp. (Trichoptera) and Caenis luctuosa (Ephemeroptera) to be characteristic for the lakewards edges of reed stands. Shore sites were indicated by Valvata cristata (Gastropoda), Cloeon dipterum (Ephemeroptera), Anabolia furcata and Limnephilus decipiens (Limnephilidae, Trichoptera), whereas for the reed stand centers no indicator taxa were found. Overall, we can conclude that the taxonomic composition of macroinvertebrate communities distinctly differs between shore and lakewards sites within reed stands and that these differences are most likely due to differences in oxygen concentrations and the occurrence of COM and CWD. These results have implications for the selection of sampling sites with respect to ecological assessments as well as for the conservation, restoration and management of reed stands.