Trophic position of bottom-feeding fish in the Upper Paraná River floodplain
2009
The δ15N composition of bottom-feeding fish (iliophagous = Apareiodon affinis, Cyphocharax nagelii, Prochilodus lineatus, Steindachnerina brevipinna and S. insculpta; detritivorous = Loricariichthys platymetopon and Liposarcus anisitsi; benthophagous = Satanoperca pappaterra and Hoplosternum littorale) and their primary food sources were investigated in the upper Parana River floodplain during rainy seasons in different environments (lotic and lentic). Two hypotheses were tested: i) that the trophic position and isotopic values of the investigated organisms (fish and food resources) vary spatially; and ii) that trophic position and isotopic compositions differ among iliophagous, detritivorous and benthophagous fish. C4 macrophytes, periphyton and phytoplankton were isotopically different in sites analyzed. Significant isotopic differences occurred in the species of each trophic category. Spatial differences were observed in the isotopic composition of P. lineatus and L. platymetopon, whose values were more enriched in the Parana River and Pau Veio Lake. Significant spatial differences in trophic position were observed for L. platymetopon and H. littorale, which presented the highest values in the Parana and Baia rivers, respectively. Trophic positions were significantly different among the species that composed each trophic category. These findings demonstrate that in energy-flow studies in detrital food chains generalizations concerning the grouping of fish into trophic categories and/or habitats should only be carried out after careful investigations of the local/specific trophic dynamics of the organisms. A composicao de δ15N de peixes exploradores de fundo (iliofagos = Apareiodon affinis, Cyphocharax nagelii, Prochilodus lineatus, Steindachnerina brevipinna e S. insculpta; detritivoros = Loricariichthys platymetopon e Liposarcus anisitsi; e bentofagos = Satanoperca pappaterra e Hoplosternum littorale) e suas fontes alimentares foram investigadas na planicie de inundacao do alto rio Parana durante a estacao de chuvas em ambientes loticos e lenticos. Duas hipoteses foram testadas: i) que a posicao trofica e os valores isotopicos dos organismos investigados (peixes e fontes alimentares) variam espacialmente; e ii) que a posicao trofica e a composicao isotopica diferem entre os peixes iliofagos, detritivoros e bentofagos. Macrofitas C4, perifiton e fitoplâncton foram isotopicamente diferentes entre os locais analisados. Diferencas isotopicas ocorreram entre as especies de cada categoria trofica. Diferencas espaciais foram observadas na composicao isotopica de P. lineatus e L. platymetopon, as quais tiveram valores mais enriquecidos no rio Parana e ressaco do Pau Veio. Diferencas espaciais significativas nas posicoes troficas foram verificadas para L. platymetopon e H. littorale, as quais apresentaram os maiores valores nos rios Parana e Baia, respectivamente. As posicoes troficas foram significativamente diferentes entre as especies que compuseram cada categoria trofica. Estes resultados demonstram que em estudos de fluxo de energia em cadeias alimentares detritais generalizacoes a respeito do agrupamento de peixes em categorias troficas e/ ou habitats devem ser conduzidos somente apos investigacoes criteriosas da dinâmica trofica local/ especifica dos organismos.
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