Relações tróficas entre peixes e presas invasoras em reservatórios do rio Grande, bacia do alto rio Paraná

Abstract

Among the various impacts caused by non-native aquatic invertebrates, interactions with native species and changes in the food web seem to be of particular importance, since these aspects may reveal the presence of natural enemies as predators, as well as changes in the energy dynamics of the ecosystem. The main objectives of this thesis were: (i) to evaluate experimentally the potential of a native fish species as a controlling agent of Limnoperna fortunei in a confined artificial environment, (ii) to quantify the importance of non-native prey in terms of consumption and isotopic contribution, for the ichthyofauna of the Volta Grande reservoir, upper Paraná river basin and (iii) to compare the composition of benthic macroinvertebrates, the trophic structure of the ichthyofauna and isotopic signature of common fish between two reservoirs, in the presence and absence of non-native prey species. For these, a short-time predation experiment was carried out at a fish farm and fish and benthic macroinvertebrates were collected in two reservoirs locat ed on the Grande River. To obtain data on the consumption and assimilation of non-native prey by fish in Volta Grande, conventional dietary methods and isotopic analyzes of the muscle tissue of fish and their prey were performed. In order to compare these results with those obtained in a reservoir where some non-native prey are absent, fish and macroinvertebrates samples were carried out in Funil reservoir, with the fish being submitted to the same analysis procedures described to Volta Grande. Exposure to predation by adults of Leporinus elongatus consistently reduced L. fortunei biomass and the level of impact on this increased significantly with increasing predator densities and periods of exposure. The results obtained in Volta Grande revealed a trophic structuring strongly composed of non-native species and the isotopic analyzes indicated that at least half of the carbon used by most fish was derived from non-native prey. With the data obtained in two similar reservoirs it was possible to detect that in Volta Grande most of the energy flow between benthic organisms and the fish community occurred through invasive species, especially L. fortunei and M. amazonicum, step that in Funil was shared between invaders and natives. From the above results it was possible to validate the important role of predation as a subsidy for the biological control in confined area and the potential use of native predators for this activity. In addition, it demonstrated strong evidence of the role played by non-native prey in the natural environment as an important part of the diet and supply of carbon to fish biomass. Finally, the comparative study between invaded and noninvaded systems with similar fish communities, provided conditions of reference to evaluation of the effects showing to be an effective strategy.