CONICET | Buscador de Institutos y Recursos Humanos

Biological criterioa are needed to provide information about the effects of the human impact in coastal marine environments. Benthic foraminifera are likely to leave fossil remains in the sediments wich can be compared withe their living counteparts. Eight subtidal surface samples were collected, as a basis fro the interpretation of three sedimentary sections along Bahía Blanca estuary (38°42´-38°49´ & 62°26´-62°8´)(Buenos Aires, Argentina). The main objetive of this study is to assess the foraminiferal response to environmental changes during the last 6000 yrs BP., comparing fossil assemblages with modern ones and with geochemical data. Fossil foraminferal fauna in the Bahía Blanca estuary were of relatively low diversity and dominated by species of the genus Elphidium Montfort, 1808 and Buccella peruviana (d´Orbigny 1839) among others. Differences between faunas collected in fossil sequences and in recent ones include a strong decrease in relative abundance of Buccella peruviana over all Bahia Blanca estuary; the increasing presence of Ammonia sppm and the appearance of abundant specimens of Haynesina germanica (Ehremberg, 1840), which were absent all along the fossil record for the area. Previous studies of modern foraminifera assemblages demonstrate the Haynesina germanica is widely distributed and abundant thourght the modern habitats of the estuary. Comparative faunal assemblage analysis from date core sample material fron within Bahia Blanca estuary shows that the species has not been present for at least the last 6000 years. This support the hypothesis that the invasion of H. germanica (taht has been accidentally introduced outside its natural range as a probable result of ballast water and /or shipping activities) is ultimately resulting in the biotic homogenization of foraminiferal fauna.

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