Foraminifera and geomicrobiology as indicators of the environmental recovery in a mangrove affected by oil spills in the Guanabara Bay (Brazil).

Foraminifera could be used as indicators to evaluate the impacts of oil spills because the crude oil causes several disturbances on the development and reproduction of the species. However, little is known about the relationship between mangrove species and this pollutant. Foraminiferal assemblages were studied in 22 surface sediment samples collected from a mangrove in Guanabara Bay (Brazil) that was severely impacted by an oil spill six years earlier. The foraminiferal responses to the environmental stress helped to determine the most degraded areas. Elevated concentrations of aromatic compounds and potentially bioavailable heavy metals, with contamination levels up to nine times higher compared to the pre-industrial period in the Guanabara Bay. The dominance of anaerobic bacteria, and high esterase enzyme activity (ESTE) suggest that the bacterial community is metabolizing the hydrocarbons in the sediments. Despite these stressors, density and diversity of living foraminifera are comparable to values observed in less impacted Brazilian mangroves. Species distribution patterns reveal an environmental gradient across the mangrove with numerous species increasing their relative abundance towards the areas topographically lower and with higher levels of pollutants and ESTE. Specifically, Caronia exilis, Tiphotrocha comprimata, Ammobaculites exiguus, Textularia paranaguaensis, Ammotium cassis, Ammobaculites dilatatus, Polyssaccamina hipohalina, Siphotrochammina lobata, Ammonia tepida, Ammotium morenoi, Miliammina fusca, Entzia macrescens, Trochammina squamata and Paratrochammina clossi are inferred as pollution-tolerant taxa. This integrated geochemical, microbiological and ecological approach applied to assess the sediment quality in a complex ecosystem has important implications for the use of living foraminifera in recovery stage assessments and biomonitoring plans.