Impact of exotic rainbow trout on the benthic macroinvertebrate community from Andean-Patagonian headwater streams.

LEONARDO BURIA,; RICARDO ALBARIÑO,; DÏAZ VILLANUEVA, VERÓNICA; BEATRIZ ESTELA MODENUTTI O BEATRIZ MODENUTTI O B. MODENUTTI; ESTEBAN BALSEIRO,

ARCHIV FUR HYDROBIOLOGIE

Scheizerbart'sche Verlagsbuchhandlung

Lugar: Stuttgart; Año: 2007 vol. 68 p. 145 - 154

0003-9136

Introduction of salmonids is a common and widespread practice in rivers and lakes of Patagonia, buttheir impacts remain poorly understood. We analyse the effect of exotic introduced salmonids (rainbow troutOncorhynchus mykiss) on the benthic macroinvertebrate community of low order streams. We conducted a fieldsurvey in three headwater streams (Challhuaco, Cascada and Pescadero streams) in the northern Andean-Patagonianregion (around 41° S and 1500m above sea level). The streams are canopied by deciduous Nothofagus pumilioforest. On each system, we established fishless and contiguous fish sites separated by waterfalls that limit fishaccess to upper sections. At each site we determined benthic macroinvertebrate size, taxonomic and functionalstructure in addition to trout gut contents. In the presence of trout, we observed significant shifts in invertebratebody size towards smaller individuals, thus a decrease in total macroinvertebrate biomass was observed. Wefound that large taxa (Klapopteryx kuscheli, Tipula sp.) and active swimming species (Metamonius anceps andHyalella curvispina) were reduced in abundance or were absent in reaches with trout. At the same time, we foundthat trout positively selected large size classes of invertebrates. As a consequence of species losses, benthic communitystructure changed drastically in the presence of trout: shredders were the feeding group most affected negatively(?68 %) followed by scrapers. The reduction of shredders may suggest a potential effect on Nothofagusleaf litter breakdown and hence, supply of FPOM to downstream reaches.