Ecologia trófica da assembléia de peixes em um rio intermitente do Semiárido

Abstract

Fish are the main consumers of semiarid rivers and streams, which have intermittent character and are structured by critical variations in the hydrological regime. The knowledge of the relationships between hydrological variations, habitat structure and fish are important for the proper conservation of these ecosystems. The hypotheses tested in this study were that (1) the habitat is spatiotemporally variable and that its structure influences the composition of the diet of the species and (2) the fish assemblage present low degree of overlap in the exploitation of food resources. The sampling plan consisted of three sampling units (UA's) in the sub-basin Seridó river of the Piancó-Piranhas-Açu river basin, in which four samples were collected, two during wet season (April and July 2007) and two in the dry season (November 2007 and January 2008). In each UA were collected data on fish and habitat structure. In the laboratory, the fish gut content was assessed and quantified according to the Hyslop's method of indirect volume. Statistical analyzes were made in the program PC-ORD. Regarding the data of habitat structure, the NMS analysis showed segregation between UA's, a result confirmed by the significance test MRPP. The indicator species analysis (ISA) identified as important habitat components for the separation of UA's: mud (Catureré), macrophytes and algae (Riacho da Serra) and sand (Poço dos Patos). In the analyzes of diet composition of species, significant differences were identified between carnivores and omnivores and between UA's, supported by MRPP test. The ISA has revealed that the most important items for omnivores were fragments of insects, sand, Diptera, unidentified plant material, algae, seeds, detritus and Coleoptera, for carnivores Macrobrachium sp. and fragments of fish. The data report that both habitat structure as the diet of the species varied spatially (UA's), but not temporally (seasons). Additionally, the diet of trophic groups showed low degree of dietary overlap, being influenced by the composition of marginal habitat and the composition of the substrate, which shows trophic opportunism.