Hydraulic microhabitats and the distribution of macroinvertebrate assemblages in riffles

Abstract

1. The influence of hydraulic conditions on the spatial distribution of macroinvertebrate assemblages was investigated in three riffles in a perennial Australian river. 2. Velocity, depth and variability of substrate roughness were measured at each of 56 macroinvertebrate sampling locations. Complex hydraulic variables (roughness Reynolds number, shear velocity, Froude number) were calculated from combinations of two or three of the directly measured variables. The biological significance of directly measured and complex hydraulic variables was determined by a combination of univariate and multivariate statistical procedures. 3. Macroinvertebrate abundance, number of taxa and community composition were significantly different between the identified roughness Reynolds number, Froude number, velocity and shear velocity microhabitats throughout the studied riffles. 4. Regression analysis showed macroinvertebrate abundance and number of taxa were negatively related to roughness Reynolds number, shear velocity, velocity and Froude number. Depth was negatively related to abundance. In general, the majority of the macroinvertebrate community preferred the areas of riffles with the lowest near-bed turbulence. 5. Roughness Reynolds number explained more of the spatial variation in invertebrate abundance, number of taxa and community composition than the other hydraulic variables, either directly measured or calculated. Of the directly measured variables, velocity had the greatest explanatory power, which was marginally less than roughness Reynolds number and shear velocity. 6. This study demonstrated that small-scale differences in hydraulic conditions created by combinations of velocity, depth and substrate roughness have an important role in the spatial distribution of macroinvertebrate assemblages in riffle habitats.

Spatial and temporal patterns of macroinvertebrates in drift and on substrate of a mountain stream (Cordoba, Central Argentina)

“…In Achiras stream, the highest densities of drift were recorded in winter and spring, when the current velocity and precipitations exhibited the lowest values. Our results are consistent with those reported by other authors for Neotropical streams and rivers of medium order (Ramírez and Pringle 1998b;Corigliano et al, 1998). On the other hand, lower densities of drifting organisms were recorded during periods of and found that they are dissimilar.…”

“…The presence of these taxa represents an important contribution because they increase the taxonomic richness and help to complement the baseline biodiversity information of a river system (Svendsen et al, 2004). The magnitude of drift responses to changes in flow depends on the time in which the last fluctuation occurred (Corigliano et al, 1998). In stable hydrological conditions over prolonged time periods, organisms have higher opportunities to associate with specific microhabitats and thus increase their densities (Poff and Ward, 1991).…”

“…Our results clearly segregated drift assemblage of low water period from high water assemblage. Considering the precipitations accumulated in periods prior to sampling, the drift density is low because the spates, caused by rains, denude the benthic community; therefore the high flows have a diluting effect on the bottom fauna (Corigliano et al, 1998).…”

“…Traditionally, the drift phenomenon has been studied on a limited spatial scale such as one river (Svendsen et al, 2004) or at stream reach level. However, research on changes in composition and structure between fluvial habitats and the factors contributing to this variation is scarce (Leung et al 2009;Boyero and Bosch, 2002;Brooks et al, 2005). Drift studies conducted in Córdoba province (Argentina) have shown that, in a braided river reach, mayflies, chironomids and oligochaetes were the dominant groups with a distinct seasonal variation (Gualdoni et al, 1991;Corigliano et al, 2001).…”

Change does not happen overnight: a case study on stream macroinvertebrates

“…Velocity was the most important variable to be related with the macroinvertebrate composition in both cases. This variable has already been demonstrated as one of the most important factors of macroinvertebrate community (Boyero and Bailey, 2001;Brooks et al, 2005;Guareschi et al, 2014). The importance of the CPOM resource for stream macroinvertebrate distribution has been previously stressed in similar Apennine ecosystems, particularly in relation to shredders distribution (Fenoglio et al, 2005).…”