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

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Introduction of salmonids is a common and widespread practice in rivers and lakes of Patagonia, but their impacts remain poorly understood. We analyse the effect of exotic introduced salmonids (rainbow trout Oncorhynchus mykiss) on the benthic macroinvertebrate community of low order streams. We conducted a field survey in three headwater streams (Challhuaco, Cascada and Pescadero streams) in the northern Andean-Patagonian region (around 41° S and 1500 m above sea level). The streams are canopied by deciduous Nothofagus pumilio forest. On each system, we established fishless and contiguous fish sites separated by waterfalls that limit fish access to upper sections. At each site we determined benthic macroinvertebrate size, taxonomic and functional structure in addition to trout gut contents. In the presence of trout, we observed significant shifts in invertebrate body size towards smaller individuals, thus a decrease in total macroinvertebrate biomass was observed. We found that large taxa (Klapopteryx kuscheli, Tipula sp.) and active swimming species (Metamonius anceps and Hyalella curvispina) were reduced in abundance or were absent in reaches with trout. At the same time, we found that trout positively selected large size classes of invertebrates. As a consequence of species losses, benthic community structure 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 Nothofagus leaf litter breakdown and hence, supply of FPOM to downstream reaches.
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Keywords: ANDEAN PATAGONIAN HEADWATERS; BENTHIC MACROINVERTEBRATES; BIOLOGICAL INVASION; FUNCTIONAL FEEDING GROUPS; SALMONIDS

Document Type: Research Article

Publication date: 2007-02-01

More about this publication?
  • Fundamental and Applied Limnology is an international journal for freshwater research in the widest sense, including problems of marine biology and brackish water research. Papers dealing with ecological topics are especially welcome in association with experimental or physiological studies. All papers published in this journal are subject to peer review.

    Archiv für Hydrobiologie, now Fundamental and Applied Limnology has been published continuously since 1906.

    Volumes prior to vol. 168 were published under the previous title Archiv für Hydrobiologie.
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