Insights into the Ecology of Foraminifera from the Most Hypersaline Lagoon in Brazil: Vermelha Lagoon

Living foraminiferal assemblages were studied in 56 samples collected in Vermelha Lagoon considered the most hypersaline lagoon in Brazil. The study aimed to improve knowledge about the biodiversity and ecology of foraminifera in confined hypersaline environments and to assess the quality status of this ecosystem. The results revealed that foraminiferal assemblages were dominated by miliolids, mainly Quinqueloculina seminula, and Ammonia tepida (Rotalioidea). This assemblage was different from those usually reported in hypersaline lagoons with bottoms consisting of carbonate sand-rich sediments. Salt production in this lagoon produces hypertrophic conditions in the sediment, which has a severe impact on the foraminiferal community. The distribution of miliolid species is related to organic matter mainly associated to higher concentrations of carbohydrates. The rotaliids Haynesina concentrica, Bolivina variabilis, and Rosalina floridana were positively related to protein and lipid concentrations. The species Massilina protea, A. tepida, and Bolivina striatula were related to high salinity, while Miliolinella subrotunda presents a negative relationship to this variable. Based on the distribution of foraminiferal species and their responses to the analyzed environmental variables, five regions with different ecological characteristics and sediment trophic states were identified. Among these, the central pond can be considered the most favorable environment. The western pond and the vicinity area of stromatolite field in the eastern pond, with a high concentration of lipids and proteins, were the least favorable region due to eutrophication status.

Automated summary

This study examined living foraminiferal assemblages in Vermelha Lagoon, the most hypersaline lagoon in Brazil, in order to understand the biodiversity and ecology of foraminifera in confined hypersaline environments and assess the ecosystem's quality status. The dominant foraminiferal species were miliolids, mainly Quinqueloculina seminula and Ammonia tepida, which differed from those typically found in hypersaline lagoons with carbonate sand-rich sediments. Salt production in the lagoon led to hypertrophic conditions in the sediment, severely impacting the foraminiferal community. The distribution of miliolid species was influenced by organic matter, particularly carbohydrates, while rotaliid species were related to protein and lipid concentrations. Five regions with different ecological characteristics and sediment trophic states were identified based on the distribution of foraminiferal species and their responses to environmental variables. The central pond was considered the most favorable environment, while the western pond and the vicinity area of stromatolite field in the eastern pond were the least favorable regions due to eutrophication status.