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

Hydrobiologia, Jul 2017

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.

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

In the mood for wood-habitat specific colonization patterns of benthic invertebrate communities along the longitudinal gradient of an Austrian river Florian Dossi 0 1 . Patrick Leitner . Steffen Pauls . Wolfram Graf 0 1 0 S. Pauls Senckenberg Research Institute and Natural History Museum Frankfurt , Senckenberganlage 25, 60325 Frankfurt am Main , Germany 1 F. Dossi (&) P. Leitner W. Graf IHG - Institute of Hydrobiology and Aquatic Ecosystem Management, BOKU - University of Natural Resources and Life Sciences , Gregor-Mendel-Strasse 33, 1180 Vienna , Austria 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. Community change; Macroinvertebrates; River course; Xylal; Lafnitz Introduction Structural complexity, a key aspect in the maintenance of biodiversity and stability in ecosystems, is significantly affected by instream obstacles such as boulders and logs. Micro- and mesohabitat variety within a small spatial scale is a crucial factor for a selfsustaining and diverse riverine biocoenosis (Beisel et al., 1998, 2000) . Like boulders and rocks, large wood (hereafter LW) and wood-accumulations have a strong influence on local hydraulics (e.g., Shields et al., 2001; Mutz, 2003; Manners et al., 2007; Blanckaert et al., 2014) and morphology (e.g., Gurnell et al., 1995; Keller et al., 1995; Kail, 2003; Blanckaert et al., 2014) . Unlike rocks and boulders, LW also affects the nutrient budget of a river (e.g., Bilby, 1981; Hering & Reich, 1997; Gurnell et al., 2005; Flores et al., 2011) and presents an important habitat structure that increases the density and diversity of fish and benthic invertebrate species in rivers and streams (e.g., Dudley & Anderson, 1982; Copp, 1992; Hoffmann & Hering, 2000; Pilotto et al., 2014, 2016) . Partially submerged logs serve as important land–water interfaces and oviposition sites for merolimnic insects, thereby significantly affecting their reproductive success (Dudley & Anderson, 1982; Sweeney, 1993; Hoffmann & Hering, 2000) . The importance of LW has mainly been studied in North America (e.g., Anderson et al., 1978; Harmon et al., 1986; Maser & Sedell, 1994; Abbe & Montgomery, 1996; Bilby & Bisson, 1998) as only few pristine river stretches with intact riparian vegetation and LW dynamics remain in Central Europe (Hering & Reich, 1997; Hering et al., 2000; Tockner et al., 2009) . Most studies focused on specific river sections. Information on the importance of LW for benthic invertebrate communities along the longitudinal gradient of a river is still lacking. Lotic aquatic systems are characterized by continuous changes of physical and chemical variables, hydromorphological characteristics, and corresponding shifts of aquatic communities along the river course (Vannote et al., 1980; Cushing et al., 1983) . Recent findings further show a varying availability and quality of wood habitats (e.g., total wood load, percentage of logs clustered in jams, the residence time of logs) along the longitudinal gradient of a river (Abbe & Montgomery, 2003; Wohl & Jaeger, 2009) . The emphasis of wood and river interactions depends on the overall river characteristics such as the slope or log and river size ratio (Hering & Reich, 1997; Scherle, 1999; Urbanek et al., 1999) . In smaller rhithral river sections, LW primarily affects river morphology as it has the potential to significantly alter the surrounding habitat distribution or even the river course (Hering & Reich, 1997; Urbanek et al., 1999; Kail, 2003) . The concurrent presence of other coarse abiotic substrates in upper river stretches, which also provide stable habitats for benthic invertebrate species as well as attachment sites for periphytic algae, suggest only a negligible importance of LW as unique structure in upper river stretches. Effects on surrounding habitats and the retention of organic matter (...truncated)


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Florian Dossi, Patrick Leitner, Steffen Pauls, Wolfram Graf. In the mood for wood-habitat specific colonization patterns of benthic invertebrate communities along the longitudinal gradient of an Austrian river, Hydrobiologia, 2017, pp. 1-14, DOI: 10.1007/s10750-017-3307-z