Food webs of the Paraná River floodplain: Assessing basal sources using stable carbon and nitrogen isotopes

Abstract

Food webs in floodplain ecosystems may be based on a variety of aquatic, terrestrial or amphibiousfood resources. Here, we determined which of the basal resources mostly contribute to the food websin a floodplain lake of the Middle Paraná River using isotopic composition of C and N (ı13C and ı15N)of potential food sources in the Paraná floodplain (Argentina). We analyzed if organic matter sourcesisotope of C and N differ between flooding and low water seasons, and analyzed the isotopic niche repre-sentations of consumers in order to characterize niches width and intraguilds overlapping. To estimatethe contribution of different sources of carbon to primary consumers, we measured the stable isotopiccompositions of bottom sediment organic matter, coarse particulate organic matter, biofilm, suspendedparticulate organic matter, epiphyton, phytoplankton, C3 and C4 macrophytes and riparian tree leaves,benthic macroinvertebrates, aquatic orthopterans and fishes in dry and flooding seasons. The packagesStable Isotope Analysis and the Stable Isotope Bayesian Ellipses algorithm in R were calculated to comparethe C and N isotopic variability between the primary consumers and their sources. The energy sourcesavailable for benthic organisms mainly originated from autochthonous sources based on the C3 photo-synthesis pathway. The isotopic signatures of sources and primary consumers did not differ significantlybetween low and high water seasons. Our results demonstrated a higher contribution to primary con-sumers of C3 macrophytes and low contributions of C4 for herbivores; biofilm and benthic organic matterfor gatherer collectors (Oligochaeta and Chironominae); epiphyton for ephemeropterans, amphipods andfishes, whereas biofilm was the most important source for mussels.