First insights into the association of complex hydraulic variables with the abundance and richness of Elmidae (Coleoptera) in the Amazon

Abstract

Hydrological habitat associations of Amazonian macroinvertebrates remain largely unknown, especially for the beetle family Elmidae. This study provides the first insights into the association of complex hydraulic variables (shear velocity, Reynolds and Froude numbers) with the abundance and taxon richness of Elmidae in the Amazon. In a 150-m reach, a meander followed by a straight stretch, five habitats were visually identified that differed in substrate composition and water velocity. Using the Fisher-Jenks algorithm and measurements of complex hydraulic variables in this stretch, the five habitats were pooled into four hydrological classes among which we compared Elmidae genera. Greater Elmidae diversity was associated with higher hydrodynamic energy habitats and riverbed heterogeneity, with Elmidae genera being clearly associated with specific hydrological habitats. Hexacylloepus and Xenelmis were associated with meander margins and backwaters, with lower hydrodynamic energy and finer sediment. Stegoelmis, Microcylloepus, Phanoceroides, Neoelmis and Heterelmis were associated with marginal and central areas of straight stretches or the meander thalweg, with higher hydrodynamic energy, and coarser and more heterogeneous sediment. Our results may be used as a baseline for other parts of the Amazon, since we demonstrated a clear association between complex hydraulic variables and substrate diversity with the distribution, abundance and taxon richness of Elmidae. A more robust description of habitat heterogeneity using complex hydrological variables and the identification and maintenance of natural habitat heterogeneity in rivers is important for the management and conservation of Amazonian aquatic biodiversity.