Woody debris and terrestrial invertebrates – effects on prey resources for brown trout (Salmo trutta) in a boreal stream

• Published in: Environmental biology of fishes 2014-05, Vol.97 (5), p.529-542
• Main Authors: Gustafsson, Pär, Greenberg, Larry A, Bergman, Eva
• Format: Article
• Language: English
• Subjects: Animal populations; Animal Systematics/Taxonomy/Biogeography; Aquatic fauna; aquatic habitat; Aquatic habitats; aquatic invertebrates; Aquatic organisms; Biomass; Biomedical and Life Sciences; Biota; Canopies; canopy; energy flow; Environment; fauna; Food resources; foods; Forest practices; forests; Freshwater & Marine Ecology; intensive forestry; Invertebrata; Invertebrates; Life Sciences; Macroinvertebrates; Nature Conservation; Predation; Prey; recruitment; Riparian ecology; Riparian vegetation; Salmo trutta; streams; Subsidies; Terrestrial environments; Trout; Wood; Zoology
• ISSN: 0378-1909; 1573-5133
• DOI: 10.1007/s10641-014-0250-y

Intensive forestry and other activities that alter riparian vegetation may disrupt the connectivity and the flux of energy between terrestrial and aquatic habitats and have large effects on biota, especially in small streams. We manipulated the amount of in-stream wood and the flux of terrestrial invertebrate subsidies to determine how these factors affected potential food resources for drift-feeding brown trout (Salmo trutta ) in a boreal Swedish forest stream. Specifically, we followed the effects on the abundance of aquatic and terrestrial invertebrate fauna from June to August 2007. The treatments were 1) addition of wood, unmanipulated terrestrial invertebrate inputs, 2) reduction of terrestrial invertebrate inputs (using canopy covers), no addition of wood, 3) unmanipulated ambient conditions, 4) simultaneous addition of wood and reduction of terrestrial invertebrate inputs. Added wood resulted in greater biomass of aquatic invertebrate biomass, and both input and drift of terrestrial invertebrates were reduced by canopy covers. In terms of total potential prey biomass, the addition of wood with ambient levels of terrestrial invertebrate inputs had the highest standing crop of benthic, wood-living and terrestrial invertebrates combined, whereas the treatment with reduced terrestrial input and no wood added had the lowest standing crop. Our study indicates that forest practices that both reduce the recruitment of wood and the input of terrestrial invertebrates to small streams have negative effects on prey availability for drift-feeding brown trout. The positive effects of wood addition on biomass of aquatic macroinvertebrates may partly compensate for the negative effects of reduced terrestrial invertebrate subsidies.