LAUSR

Abstract Estuaries in South America commonly receive untreated effluents from nearby metropolitan areas demanding ecosystem-based management solutions to access pollutant impacts. In this study we investigated how organic enrichment in Vitoria Bay changes benthic macrofaunal isotopic signatures (δ13C and δ15N) and if highly contaminated areas would exhibit lower food web diversity. Geochemical markers of sewage input (coprostanol) revealed low to high levels of pollution in the bay area. The δ15N isotope signatures of benthic deposit-feeders and omnivores were lower in contaminated sites indicating preferential intake of raw sewage and that the effect size of sewage input changes among benthic feeding modes. Sites with high sediment coprostanol concentrations (>0.5 μg g−1) were associated with a lower abundance of basal resources and niche shrinking of the benthic food web, suggesting that eutrophication leads to a funtional loss in the sediment-water interface in this estuary. Our study revealed that pollution in the Vitoria Bay estuary has functional impacts to the estuarine food webs and support previous ascertions that stable isotopes may be a useful and low-cost method to indicate ecosystem health monitoring in estuarine ecosystems.