Ecologia trófica da ictiofauna do Rio Jaguaribe (Ceará) no cenário pré-transposição do Rio São Francisco, Nordeste, Brasil

Abstract

The trophic ecology provides information about organisms feeding habits in natural environment, making possible to understand about ecological role played by the species involved, and that enable to comprise the complexity of ecosystem trophic relations. The aim of this study was to evaluate the diet and trophic structure of the ichthyofauna from the Jaguaribe River basin, one of the biggest temporary rivers in the world, considering temporal and spatial variation. The samples were taken at the exact moment before the waters of the São Francisco River transposition arrive; thus, the scenario exposed in this study no longer exists. The samplings occurred in the dry (oct/2019) and rainy (mar/2020) seasons in the main course of the basin, totalizing nine sampling points. The sampling methods were standardized with dragnets (10 m) and cast nets (6 times for point) to catch the fishes. Water variables were taken in situ, and water was collected for the nutrient analysis. Within the 40 fish species that were collected, 26 had their food items analyzed using volumetric methods, and were grouped into nine food resources categories, that were classified into trophic guilds: Insects, Collembola, Mollusca, Decapoda, Microcrustaceans, Fish, Algae, Superior vegetal and Detritus. For the diet analysis, the food items volumes (mL) were evaluated with Permutational multivariate analysis of variance (PERMANOVA), and the niche breadth with Permutational analysis of multivariate dispersions (PERMDISP), both using the Bray-Curtis abundance distance as similarity measure. The abiotic data were ordinated by a Principal Component Analysis (PCA). The trophic structure was determined through the niche overlap, species abundance and richness to each trophic guild, and compared at temporal and spatial scales, to evaluate the presence of a longitudinal gradient. The main resources consumed by the ichthyiofauna from Jaguarive River basin were detritus and insects. There was spatial variation and temporal in the assemblage diet and trophic structure, which the spatial one between the river portions was most significant for the niche breadth. The ichthyofauna shows aggregation pattern in the rainy season, while the dry season shows a pattern of homogenized resource consumption. Jaguaribe River basin does not shows a longitudinal variation pattern, highlighting the integrative approach needed for the description of lotic environments at semiarid regions.