Variation in nitrogen and carbon isotopes in the Bahía Blanca Estuary: Implications for ecological studies in a human-disturbed system

BIANCALANA F; DUTTO, M. SOFÍA; KOPPRIO GA; LARA RJ; HOFFMEYER MS

Pucón

Simposio; 5th International Zooplankton Production Symposium; 2011

Although stable carbon and nitrogen isotopes are widely used in marine ecosystem research, this study presents the first report on their variation in the Bahía Blanca Estuary. Sampling was carried out at stations where human impact was high (Canal Vieja: CV) and low (Bahía del Medio: BM), during both the winter phytoplankton bloom and spring-summer post-bloom period. Surface water, plankton samples, and environmental variable measurements were obtained. Isotopic data were analyzed using a multivariate approach. In winter, δ13C values varied from -23.98 to -19.706? in CV and from -23.389 to -19.09? in BM. In summer, δ13C ranged from-24.83 to -18.66? and from -23.43 to -16.20?, in CV and BM stations, respectively. Generally, in both seasons, δ13C showed higher variability in consumers in BM than in CV. In winter, δ15N values ranged from 3.82 to 11.11% in CV and 7.19 to 11.72? in BM. In summer, δ15N ranged between 2.37-16.77? and 9.02 -15.19? in BM. The δ15N values indicated food sources varied from the base of the food web to consumers at both stations and in both seasons. Consequently, suspended particulate matter (SPM) and primary producer δ15N values were slightly higher than consumers. While δ13C values of SPM, producers, and consumers varied little between stations, δ15N variability was higher. These preliminary results indicate that stable isotopes are useful indicators of food types and sources, and can be used to study changes in the structure of the planktonic food web caused by anthropogenic impact in the Bahía Blanca Estuary.