Wood biofilm as a food resource for stream detritivores

Abstract

Published assimilation efficiencies indicate that leaf detritus is a more nutritious food for stream invertebrates than wood. Some studies, however, suggest that wood and wood biofilms (epixylon) may be an important but overlooked resource. We measured assimilation efficiencies of three detritivores for leaves and epixylon and compared attributes of grazed versus ungrazed wood epixylon to assess its use by detritivores. Pycnopsyche gentilis (Trichoptera), Tipula abdominalis (Diptera), and Tallaperla spp. (Plecoptera) assimilated epixylon more efficiently (26-36%) than leaf detritus (9-17%). Epixylon assimilation efficiencies were T. abdominalis . Tallaperla spp. . P. gentilis. Grazed wood had significantly lower microbial respiration rates, bacteria densities and biomass, fungal and chlorophyll a biomass, and biofilm ash-free dry mass than ungrazed wood, indicating that detritivores fed on epixylon. Detritivores ingested leaves at a higher rate (0.09-0.47 g g 21 d 21 ) than epixylon (0.04-0.07 g g 21 d 21 ). Assimilation rates, which incorporate both assimilation efficiency and ingestion rate, however, indicated that Tallaperla spp. and T. abdominalis were better able to use epixylon than leaves, whereas P. gentilis was more efficient at using leaves. Wood biofilm is readily ingested and assimilated by some stream detritivores and may serve as an important but overlooked food resource in stream food webs.

The effect of shredder community composition on the production and quality of fine particulate organic matter

“…is 4 to 253 larger than the other species used and shredder biomass was balanced explicitly among treatments. However, limnephilid caddisflies are often the functionally dominant detritivores in streams (Herbst 1980, 1982, Eggert and Wallace 2007, Creed et al 2009). Creed et al (2009) found that Pycnopsyche gentilis was both a competitive dominant and a very effective shredder.…”

Factors influencing wood mobilization in streams

“…Wood pieces provide stable substrate for invertebrates and biofilms, entrap leaves and other organic matter, afford overhead cover for fish, promote hyporheic exchange flow and transient storage, enhance hydraulic heterogeneity, and encourage pool formation and channel meandering [Angermeier and Karr, 1984;Beechie and Sibley, 1997;Gregory et al, 2003;Johnson et al, 2003;Mutz and Rohde, 2003;Eggert and Wallace, 2007;Stofleth et al, 2008]. The frequency and character of wood inputs varies in space and time [Latterell and Naiman, 2007;Golladay et al, 2007] and is strongly affected by riparian management [Flebbe and Dolloff, 1995;Angradi et al, 2004;Kreutzweiser et al, 2005;Czarnomski et al, 2008].…”

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

“…Epixylic biofilm development on incubated alder branches Driving factors of periphyton biofilm dynamics in streams reported so far were light availability and water temperature (Kiffney et al, 2003), dissolved nutrient concentrations (Tank and Dodds, 2003), grazing by invertebrates (Eggert and Wallace, 2007) and moving sediments that abrades periphyton during peak flow events (Biggs et al, 1999). Epixylic biofilms in both study streams reached maximum concentrations of chl a in May when temperature became warmer and sun light reached the stream bottom as canopy was not fully closed, yet.…”

“…Submerged wood in streams, represented mainly by medium sized branches with lengths <100 cm and diameters <10 cm (Elosegi et al, 1999), serves as habitat (Hoffmann and Hering, 2000;Benke and Wallace, 2003) and food (Pereira et al, 1982) for many invertebrate species. It provides a carbon source for wood-degrading bacteria and fungi (Gulis et al, 2008) and, finally, provides an attachment site for epixylic biofilm Sabater et al, 1998;Spa¨nhoff et al, 2006) that serves as additional food source for invertebrates (Eggert and Wallace, 2007).…”