Benthic foraminifera associated with the South Bahia Coral Reefs, Brazil

Abstract

The objective of this study was to assess foraminiferal faunas and their relationship to sediment texture and composition in the reef areas from the coastline to the 30-m isobath between the cities of Corumbau and Nova Viçosa in the extreme south of the State of Bahia. Cluster analysis of the species, identified from 38 samples of surface sediments, revealed a strong correlation with grain size. The principal relationships established between these species and the sediments were the following: (i) Amphistegina lessonii and Peneroplis carinatus were abundant in sandy carbonate sediments and (ii) Ammonia beccarii, Elphidium poeyanum, Pyrgo subsphaerica, Quinqueloculina disparilis curta and Q. lamarckiana were abundant in mixed sand and mud, whether carbonate or mixed carbonate and siliciclastic. The fluctuation in the richness index among samples indicated microenvironmental areas that were unfavorable for some foraminiferal species. Local hydrodynamic conditions result in environments with greater energy where finer sediments, together with many foraminiferal species, have been removed. In more protected areas, weaker hydrodynamic conditions permit the accumulation of fine sediments and organic matter, making the environment suitable for diverse forms of foraminifera. In general, faunal composition is typical of tropical carbonate platforms, where the reef structures provide a variety of microenvironments that account for the variations observed in the foraminiferal fauna.