CONICET | Buscador de Institutos y Recursos Humanos

Biological criteria are needed to provide information about the effects of human impact in coastal marine environments. Benthic foraminifera are likely to leave fossil remains in the sediment which can be compared with their living counterparts. Eight subtidal surface samples were collected, as a basis for the interpretation of three sedimentary sections along the Bahía Blanca estuary (38°42'-38°49?S & 62°26?-62°8?W) (Buenos Aires, Argentina). The main objective 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 foraminiferal faunas in the Bahía Blanca estuary were of relatively low diversity and dominated by species of the genus Elphidium de 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 Bahía Blanca estuary; the increasing presence of Ammonia spp. and the appearance of abundant specimens of Haynesina germanica (Ehrenberg 1840) which were absent all along the fossil record for the area. Previous studies of modern foraminiferal assemblages demonstrate that Haynesina germanica is widely distributed and abundant throughout the modern habitats of the estuary. Comparative faunal assemblage analysis from dated core sample material from within the Bahía Blanca Estuary shows that the species has not been present for at least the last 6000 years. This supports the hypothesis that the invasion of H. germanica, (that 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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