CS35 Trophic Dynamics
Date: Wednesday, June 12, 2002
Location: Poster Session - VCC
 
CalheirosDF, EMBRAPA Pantanal and Centro de Energia Nuclear na Agricultura-USP, Corumba and Piracicaba, Brazil, deborafc@cena.usp.br
Hamilton, S, K, Michigan State University, Hickory Corners, USA, hamilton@kbs.msu.edu
Martinelli, L, A, CENA-USP, Piracicaba, Brazil, zebu@cena.usp.br
Moreira, M, Z, CENA-USP, Piracicaba, Brazil, mmoreira@cena.usp.br
Oliveira, M, D, EMBRAPA, Corumba, Brazil, mmarcia@cpap.embrapa.br
Barbosa, D, S, UFMS-CNPq, Corumba, Brazil, domingos@sc.usp.br
 
STABLE CARBON AND NITROGEN ISOTOPES IN AUTOTROPHS AND CONSUMERS FROM THE PARAGUAY RIVER FLOODPLAIN, PANTANAL WETLAND, BRAZIL
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The food web of the Pantanal floodplain in Brazil was investigated during a complete hydrologic cycle using stable isotope ratios of carbon (d13C) and nitrogen (d15N). Autotrophs analyzed included microalgae (as sestonic and epiphytic particulate organic matter - POM), macroalgae and emergent and submersed plants (mostly C3). Consumers included pleustonic, planktonic and benthic invertebrates. POM samples were separated for isotopic analysis by density gradient centrifugation. C:Chlor ratios less than 100 indicated relatively pure algae and those samples ranged in d13C from -34.5 to - 27 per mil and in d15N from -8.5 to 6 per mil. The consumers ranged in d13C from -43 to -20 per mil and in d15N from -2 to 12 per mil. The filterers ranged from -43 to -32 per mil for d13C and -2 to 12 for d15N. The balance of evidence suggests an important role of microalgae in sustaining food webs although direct measurements of POM are not consistent with the consumers, despite attempts to remove detritus. Selective feeding and/or assimilation of POM most likely explain the discrepancies. Grants: FAPESP (# 99/09665-6) and CNPq (# 141193/2000-0)