Morphological abnormalities of foraminiferal tests in Brazilian environments: comparison between polluted and non-polluted areas

We investigated morphological abnormalities of Recent benthic foraminiferal tests in paralic environments of Brazil from two estuaries (Rio Guaraú and Rio Una located in the tropical forest) which are not affected by human activities in comparison to one polluted estuary (Baixada Santista), and one hypersaline lagoon (Araruama). The highest percentage of abnormal tests occurred in Rio Una (29%) and was caused by decalcification/recalcification processes resulting from natural periodical acidification. In the Rio Guaraú, percentages of abnormal tests reached 10%. The strong hydrodynamics in this estuary induced damage in living foraminiferal tests and the shape of the tests resulting from the regeneration of a damaged chamber, was often abnormal. In the lagoon of Araruama, percentages of abnormal tests reached 24%. Here, hypersalinity and strong salinity variations seem to perturb the test construction of foraminifers. In the most polluted estuary (Baixada Santista), lower percentages of abnormal tests occurred (0–7% with only one station reaching 12%). In this paralic environment, it is difficult to distinguish between the effect of natural stress and anthropogenic impact. Our study shows that higher percentages of abnormal tests occur in non-polluted areas than in polluted areas. Thus, the relative abundance of abnormal tests used as a bio-indicator of pollution in paralic environments, which are subject to strong natural stress, must be handled with care. Nevertheless, the relative abundance of abnormal tests is a useful proxy for the reconstruction of paleoecological changes in stressed paleoenvironments.