In the mood for wood-habitat specific colonization patterns of benthic invertebrate communities along the longitudinal gradient of an Austrian river

Abstract

Instream large wood (LW) constitutes an indispensable element of natural river ecosystems. It affects local hydraulics, morphology, nutrient budget, overall habitat complexity, and dynamics. Despite numerous studies about LW as a habitat for benthic communities, information on the varying importance along the longitudinal gradient of a river is lacking. The focus of this study is therefore to investigate general differences between lithal and xylal colonizers and to further investigate trends along the river course. We analyzed lithal and xylal communities at ten sites along the medium-sized Lafnitz River in Southeast Austria. Our results significantly show (1) a general differentiation between lithal and xylal communities, (2) an increasing distinction of the lithal and xylal fauna along the longitudinal gradient of the river, and (3) a distinct correlation between the distance from source and the number of exclusive xylal and nowadays predominantly rare taxa. The presence of LW is therefore directly linked to higher aquatic biodiversity compared to rocky substrates and presents a unique element for river restoration, especially in lower river sections.

Age matters: substrate-specific colonization patterns of benthic invertebrates on installed large wood

“…Samples were exposed for 6 weeks and previous studies showed that colonization on installed substrates peaks at approximately two to 6 weeks the latest (e.g., Nilsen and Larimore 1973;O'Connor 1992;Spänhoff et al 2000). Comparisons with a previously conducted study at the Lafnitz River, which focused on natural instream wood (see Dossi et al 2018) further support our results. Recorded invertebrate density and biomass were on a comparable level but on average higher in the present study on the installed logs (1655 Ind/m 2 vs. 2437 Ind/m 2 ; 19.2 g/m 2 vs. 29.6 g/m 2 ).…”

“…An additional distinction of our samples between different substrates revealed discrete benthic invertebrate density and diversity differences, with lowest values on concrete, followed by fresh and peak values on rotten wood. Only at site A, no clear differences were evident between the substrate types, which emphasizes the results of Dossi et al (2018). Their study showed that the importance of LW as unique habitat structure significantly changes along the longitudinal gradient of a river.…”

“…Further, wood characteristics such as the state of decay received little attention. Detailed results varied greatly but nonetheless consistently showed higher benthic invertebrate densities and diversities on wood compared to adjacent lithal habitats (e.g., Benke et al 1984;Smock et al 1989Smock et al , 1992O'Connor 1991;Piegay and Gurnell 1997;Hoffmann and Hering 2000;Spänhoff et al 2000;Grafahrend-Belau and Brunke 2005;Milner and Gloyne-Phillips 2005;Coe et al 2009;Pilotto et al 2016;Dossi et al 2018).…”

“…Previous studies have already stressed the beneficial effects of instream wood structures on local river hydraulics (e.g., Shields et al 2001;Mutz 2003;Manners et al 2007), hydromorphology (e.g., Gurnell et al 1995, Kail et al 2007, Blanckaert et al 2014, nutrient balance (e.g., Bilby and Bisson 1998;Gurnell et al 2005;Flores et al 2011) and habitat diversity (e.g., Dudley and Anderson 1982;Hering and Reich 1997). Submerged LW provides essential habitats which are existential for many xylobiont species (Anderson et al 1978;Hoffmann and Hering 2000) and are of increasing importance along the river course (Dossi et al 2018). LW further offers vital aquatic- terrestrial interface areas and oviposition sites, significantly promoting the reproductive success of merolimnic invertebrate species (Dudley and Anderson 1982;Sweeney 1993;Hoffmann and Hering 2000).…”

The importance of a constructed near-nature-like Danube fish by-pass as a lifecycle fish habitat for spawning, nurseries, growing and feeding: a long-term view with remarks on management

“…This is in line with one of the key elements of ecology, namely, that habitat heterogeneity increases biodiversity (Ricklefs and Schluter 1993). Additionally, large organic debris is often added from the well-stocked riparian zone, which also has a positive effect on the richness of biota (Crook and Robertson 1999;Dossi et al 2018). Noteworthy is the stagnant sidearm, which is clogged by a beaver dam, with its calm-water conditions that rarely exist in by-passes.…”