Eutrophication processes and trophic interactions in a shallow estuary: Preliminary results based on stable isotope analysis (δ13C and δ15N) |
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Authors: | Paulo Cesar Abreu César S B Costa Carlos Bemvenuti Clarisse Odebrecht Wilhelm Graneli Alexandre M Anesio |
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Institution: | 1. Department of Oceanography, Federal University of Rio Grande-FURG, Cx.P. 474, 96201-900, Rio Grande, RS, Brazil 2. Department of Limnology/Ecology, Lund University, S-223 62, Lund, Sweden 3. Institute of Biological Sciences, University of Wales, SY23 3DA, Aberystwyth, Ceredigion, U.K.
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Abstract: | Stable isotopes ratios (δ13C and δ15N) were measured in primary producers and consumers of two bays with contrasting eutrophic conditions in the Patos Lagoon
estuary, southern Brazil: the Justino bay, a more pristine ecosystem, and the Mangueira bay, a heavily polluted region that
receives the Rio Grande city sewage and effluencts of several industries. δ13C values of organisms collected in both subsystems were not different, but δ15N values had significant statistical differences, ca. 3.5‰ higher in the Mangueira bay. It is likely that primary producers
and consumers in this subsystem are greatly influenced by higher nitrogen input due to domestic and industrial sewages. The
stable isotope analysis also corroborated several trophic interactions previously established by gut content analysis, and
due to its higher sensitivity, it was possible to better determine the contributions of different primary producers and detrital
fractions to the consumers' diets. It was confirmed that plant detritus represents the main food source for most organisms.
The stable isotope analysis also demonstrated that detritivorous benthic organisms in the same habitat have distinct diet
compositions, with differential consumption of C3 and C4 plants. This technique showed that some consumers that eat detritus
do not have in their stable isotopic signature any relationship with that of plants. It is likely that these consumers assimilate
their carbon and nitrogen from other sources like microalgae or microorganisms that colonize decaying plants. |
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