Abstract
Benthic macroinvertebrates constitute the link between organic matter input in streams and fishes. However, the possibility of influence of predators on the invertebrates is still a controversial issue. The possibility of alteration of the benthic community by the modification in predation in a stream in the South of Brazil was studied by means of an exclusion experiment under semi-natural conditions. The exclusion showed an increase in the abundance of Plecoptera in the river where the rainbow trout was introduced, the larvae of Trichoptera also increased in abundance in the units of fish exclusion. This difference does not confirm the pressure applied by the trout on the benthic macro fauna due to differences in ichthyofauna and in the habitat of both rivers. Nevertheless, it points to the need for the development of studies concerning the trophic relations and the possible effects of this introduction in the aquatic biota.
Highlights
Benthic macroinvertebrates have an essential role in the maintenance of river communities by the linkage established in the food chain between organic matter and fishes (Hauer and Resh, 1996)
Aquatic biota is structured through this linkage according to the river continuum concept proposed by Vannote et al (1980)
The aim of this work is to verify the consequences of predation by fish on the benthic macroinvertebrates community of low order streams in the south of Brazil by means of an exclusion experiment, and to identify differences between streams with presence and absence of the exotic rainbow trout species (Oncorhynchus mykiss (Walbaum, 1792))
Summary
Benthic macroinvertebrates have an essential role in the maintenance of river communities by the linkage established in the food chain between organic matter and fishes (Hauer and Resh, 1996). Amongst the factors that influence the response of prey to predator are: a) predator feeding characteristics, being that not all the taxa are affected (Billy and Usseglio-Polatera, 2002); b) size of prey and substrate type, presenting a higher or lower degree of shelter sites (Bechara et al, 1993) and c) types of habitats, which may have a differentiated effect, taking into consideration that in habitats made up of riffles and rapids, colonization rates are higher than in pools, causing a lower response to predators (Cooper et al, 1990). Amongst the factors that influence the response of prey to predator are: a) predator feeding characteristics, being that not all the taxa are affected (Billy and Usseglio-Polatera, 2002); b) size of prey and substrate type, presenting a higher or lower degree of shelter sites (Bechara et al, 1993) and c) types of habitats, which may have a differentiated effect, taking into consideration that in habitats made up of riffles and rapids, colonization rates are higher than in pools, causing a lower response to predators (Cooper et al, 1990). Dahl (1998) considers the control of macroinvertebrate density in rivers and streams by fishes as a controversial issue, but the fish certainly exert influence on the behavior of the prey, sometimes to sub-lethal levels
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