Foraminiferal assemblage structure from Brazilian tropical urbanized beaches (~7°S)

Abstract

Foraminifera are diversifi ed protists with high ecological and bioindicator importance. Physical-chemical parameters of the environment can be evaluated through the taphonomic analysis of the test coloring, because once they settle in the sediment their tests begin to behave as sedimentary particles. Five urbanized tropical Brazilian beaches were sampled in this study in order to characterize the diversity, abundance, taxonomic and taphonomic structure of Foraminifera assemblages. General environmental characterization such as granulometric analysis, temperature and salinity was also performed. A total of 69 foraminiferan species were found, dominated by Quinqueloculina lamarckiana, Archaias angulatus, Amphistegina lessonii, Ammonia tepida and Eponides repandus. A large predominance of dead tests (>90%) was found, and only them were considered in further analyses. The cluster based on the taxonomic composition formed two groups, separating Miramar from the other beaches. Miramar was dominated by Ammonia tepida (18.9%), Sorites marginalis (16.8%), Quinqueloculina lamarckiana (13.9%) and Textularia agglutinans (10.2%), and had the highest density, number of species and diversity, what may be related with the sheltered nature of this beach and the dominance of fi ne sand. The other four beaches have high oceanic infl uence and the medium and coarse sand predominated. In these beaches Quinqueloculina lamarckiana dominated, representing between 30.9 and 38.7% of total foraminiferans. The taphonomic analysis indicates that Miramar presents a high deposition of tests and a low hydrodynamic energy, since the majority of tests were white. In Bessa, Manaíra and Seixas most of the tests were brownish, which is characteristic of beaches with high hydrodynamic energy, which causes the tests to be constantly brought to the oxidation zone.