This study presents the first comprehensive checklist and autoecological assessment of living benthic foraminiferal species from tropical estuaries along the Brazilian Cocoa Coast. A total of 55 surface sediment samples collected from the Contas, Cachoeira, and Almada estuaries yielded 18,659 individuals belonging to 67 species, 36 genera, and 22 families. Taxonomic identification was supported by scanning electron microscopy images, providing a detailed reference framework for the region. Beyond the taxonomic inventory, weighted averaging was used to estimate species-specific environmental optima and tolerance ranges for key physicochemical and sedimentological variables. Thirty-nine species occurring at four or more sampling stations were retained for comparative ecological assessment. The results indicate that species distributions were strongly associated with salinity, sediment texture, and organic matter-related variables. The highest salinity optima were recorded for Elphidium discoidale, Haynesina germanica, and Bolivina striatula, whereas Miliammina fusca and Polysaccammina ipohalina were associated with strongly freshwater-influenced conditions. Sediment grain size was also an important structuring factor. Quinqueloculina lamarckiana and Miliolinella subrotunda showed high optima and comparatively restricted ranges towards the sandy end of the gradient, while Textularia earlandi and Paratrochammina clossi occurred across broader sedimentary conditions. Entzia macrescens and Ammoastuta inepta were associated with fine-grained and organic-rich sediments, although the latter also exhibited broad tolerance ranges for sedimentological variables and organic carbon. The integration of optimum and tolerance metrics revealed taxa with narrow regional habitat preferences and others with broader environmental tolerances. These estimates represent realized distributions within the studied estuaries and provide a quantitative regional baseline for future biomonitoring and ecological assessment of tropical estuarine systems.
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