Estudos de estruturas tróficas e de impactos antropogênicos de córregos do sistema hidrográfico Guapi-Macacu: isótopos estáveis

Abstract

We used the natural distribution of stable isotopes of carbon and nitrogen to investigate the principal basal food resources for the food web of the forested streams of the Guapi-Macacu watershed system and we evaluated if the stable isotopes of carbon and nitrogen of aquatic consumers responded to the land use and occupation in the catchment. The hypotheses of the present work are: (1) the principal energy source for the animals from forested streams comes from autochthonous production, the periphyton; (2) the δ13C and δ15N of the aquatic consumers are positively related to the percentage of the impacted areas by agriculture, pasture and urban occupation. We collected periphyton, fine particulate organic matter and animals in twenty one streams for stable isotopes analyses of carbon and nitrogen. We used aerial photos to classify and calculate the area of human use in a radius of two hundred meters from the geographic coordinate of the collection point. Periphyton was the basal resource for: the predatory fish Characidium sp., Rhamdioglanis sp., Trichomycterus sp.; the omnivorous fish Phalloceros caudimaculatus; the grazer fish, Schizolecis guntheri; the omnivore shrimp, Macrobrachium potiuna; the omnivore crab, Trichodactylus sp.; the predators Plecoptera, Anacroneuria sp.; the predators Odonata, Aeshnidae sp. e Libellulidae sp.. The material proceeding from terrestrial vegetation was the principal source of the scraper and collector-filter Trichoptera, Phylloicus sp. and Smicridea sp., respectively. The δ13C of Rhamdioglanis sp. was marginally related to the percentage of human impact area (p=0,072; N=6). The δ13C of the Anacroneuria sp., Smicridea sp., Characidium sp., Hypoptomatinae, Macrobrachium spp., Phalloceros caudimaculatus, Scleromystax barbatus and the Trichomycterus sp. were not related to the percentage of the impacted area. Only the Macrobrachium sp. (p=0,052; N=11) and the S. barbatus (p=0,069; N=6) had their δ15N marginally related to the percentage of the impacted area. These results suggest that the δ13C e a δ15N of the aquatic consumers were not good indicators of local impact in the Guapi-Macacu watershed system.