Efeitos de plantas aquáticas invasoras e anfíbia sobre a eficiência de forrageamento e a dieta de peixes associados.

Abstract

The effects of invasive macrophytes on native aquatic communities have been an important focus in studies of ecological relationships. In this study the potential effects of invasive macrophytes on the availability of invertebrates and diet composition of associated fish were evaluated in natural habitats and experimentally. First, the effects of the invasive macrophyte Urochloa arrecta on the availability of invertebrates, diet composition and foraging efficiency of four small sized fish species associated were evaluated. The main results indicated that U. arrecta is not a feeding habitat as favorable to fish as the native Eichhornia azurea, used as control, since the abundance of invertebrates was significantly higher in the native than in the invasive and the diet composition of the four fish species also varied among macrophytes. The composition, abundance, richness and diversity of invertebrates offered by the invasive macrophyte Hydrilla verticilatta and the potencial effects on diet composition, trophic niche breadth and foraging efficiency of associated fish were experimentally investigated. The native macrophyte Egeria najas was used as control, since both are submerged and have very similar architecture and physical complexity. No evidence has been found that Hydrilla verticilatta affects the density of associated invertebrates, and as consequence, diet and foraging efficiency of fish. This means that in the natural habitat and in reasonable biomasses similar to native species (rare fact for invasive species), the invasive plant can replace the native one without causing great damages to associated fish species. In the flood period, with rising water levels, plants that colonize wet habitats may become temporarily submerged forming a new habitat for small sized fish. Therefore, the amphibian macrophyte Polygonum punctatum was investigated as a temporary foraging habitat for small sized fish species during the flood period. The information obtained indicated that the amphibian P. punctatum provides resources comparable to those provided by the non-amphibian E. azurea, adding available habitat to the aquatic community during the flood period. In conclusion, it was possible to explore the relationship between invasive plants species and native community of invertebrates and associated fish, as well as the importance of the flood period to increase available habitats for exploitation by these communities.