CONICET | Buscador de Institutos y Recursos Humanos

Stables isotopes of carbon (δ13C) and nitrogen (δ15N) are increasingly used for studying marine ecosystems and as an efficient tool for ecological and environmental research. We focused on the use of these natural isotopes abundance to determine trophic levels and food sources in estuarine planktonic food web and to trace environmental sewage impact. Two sampling station were chosen in relevant locations of the Bahía Blanca estuary: one with high anthropogenic pressure (Canal Vieja: CV) and the other with low human impact (Bahía del Medio: BM). This study was carried out in two different seasons: winter-spring (phytoplankton bloom) and spring-summer. Samples of water and plankton were obtained at surface level and some environmental variables were measured. Isotopic data from similarity matrix were analyzed using MDS (multidimensional scaling). During winter, δ13C values varied from -23.98 to -19.902 in CV station, and from -23.389 to -19.09 in BM. During summer, δ13C varied from -24.83 to -19.54 and from -23.43 to -16.20, in CV and BM, respectively. In general, δ13C showed more variability in consumers (micro-, meso- and macrozooplankton) in BM than CV, in both seasons. In winter, δ15N values ranged from 3.82 to 11.11% in CV and from 7.19 to 11.72 in BM. In summer, δ15N ranged from 2.37 to 16.77 and from 9.02 to 15.19 in BM. δ15N values varied from the base of the trophic level to consumers in both stations and seasons. Consequently, the suspended particular matter (SPM) and primary producers showed values slightly higher than consumers. While δ13C values of SPM and consumers varied low between stations, δ15N variability was higher. These preliminary results show the value of stable isotopes as ecological and environmental indicators to study seasonal features in food types and sources, as well as changes in the structure of food web caused by anthropogenic impact in the Bahía Blanca estuary.