Wood in different stream types: Epixylic biofilm and wood-inhabiting invertebrates in a lowlandversusan upland stream

Abstract

-Colonization of incubated wood samples by invertebrates and biofilm was compared between a lowland and an upland stream over a 15 month period. Invertebrate densities increased during the first weeks of incubation and then decreased to rather stable densities during the remaining investigation period in both streams. Within the first incubation weeks invertebrate numbers were significantly higher in the lowland stream. Higher dissolved nutrient concentrations and water temperatures accelerated initial epixylic biofilm development in the lowland stream. Lowest invertebrate numbers on incubated branches in the lowland stream coincided with increased discharge. Extreme low flows in the upland stream resulted in lowest invertebrate numbers on incubated wood during the study. Temporal patterns of biofilm and invertebrates indicated some interactions, but statistical significance was low, which might be caused by the variety of interacting effects. Additionally, invertebrate assemblages of in-stream wood samples were collected from four lowland and four upland streams to examine differences of epixylic invertebrate assemblages between the two stream types. Invertebrate densities were significantly higher on submerged wood from lowland streams than wood from upland streams. However, no clear differences in invertebrate assemblages found between the stream types. The study results show that introduced wood in lowland and upland streams is rapidly colonized by aquatic invertebrates and provided an attachment site for biofilms. Invertebrate numbers during the first two months of incubation significantly overestimate the invertebrate numbers found on resident in-stream wood in lowland and upland streams. Analyses of taxonomic composition of wood-inhabiting invertebrate assemblages from natural wood from lowland and upland streams revealed that each stream displayed a rather specific epixylic fauna.

Fine stream wood decreases growth of juvenile brown trout (Salmo trutta L.)

“…fine stream wood, has the potential to affect stream-living salmonids both by increasing the availability of shelters, and by offering a beneficial microhabitat for colonizing stream invertebrates. Several studies have shown that prey availability of streamliving salmonids is positively affected by the presence of instream structures (Spänhoff and Cleven 2010;Gustafsson et al 2014;Herdrich et al 2015;Enefalk and Bergman 2016b), and this greater prey availability could potentially increase salmonid growth. Also, growth can be increased due to the energetic benefits of reduced swimming costs when the salmonid forage from a focal point in a shelter, instead of foraging in faster flowing water (Fausch 1984(Fausch , 1993.…”

Effects of fine wood on macroinvertebrate drift in four boreal forest streams

“…Large wood (LW) can affect streams by changing the characteristics of flow and structure (Bilby & Ward, 1989;Beechie & Sibley, 1997), by increasing the retention of nutrients and energy (Smock et al, 1989) and by providing sites for invertebrate attachment and feeding (Eggert & Wallace, 2007;Spänhoff & Cleven, 2010). During the last century, the input of large and fine wood from the riparian zone has decreased owing to changed forestry practices and disturbance processes (Nakamura & Swanson, 2003;Crisp et al in Northcote & Hartman, 2008;Vaz et al, 2013).…”

“…The invertebrate density on the wood usually reaches a relatively stable level within 5-8 weeks, and levels off or decreases thereafter (Nielsen & Larimore, 1973;Drury & Kelso, 2000;Bond et al, 2006). However, the peak may appear as late as three months after the addition of wood (Spänhoff & Cleven, 2010). Invertebrate use of wood differs between species and functional groups.…”

“…Invertebrate use of wood differs between species and functional groups. Most invertebrates use wood as perches from which they catch food, or as substrates to attach to (Dudley & Anderson, 1982;Spänhoff & Cleven, 2010). Also, interstices and recesses of wood are important as refuges and feeding sites for the organisms (Dudley & Anderson, 1982;Drury & Kelso, 2000;Spänhoff et al, 2006).…”

“…Also, interstices and recesses of wood are important as refuges and feeding sites for the organisms (Dudley & Anderson, 1982;Drury & Kelso, 2000;Spänhoff et al, 2006). Even small pieces of FW offer a relatively large surface area for biofilms (O'Connor, 1991) that provide food for grazing invertebrates (Dudley & Anderson, 1982;Wallace & Webster, 1996;Eggert & Wallace, 2007;Spänhoff & Cleven, 2010). Thus, wood is used by a wide variety of stream invertebrate species, and the invertebrate fauna that colonize wood typically reflects the dominant taxa of zoobenthos and drift in the stream (Benke & Wallace, 2003).…”