| Resumo: |
Species composition, abundance and spatial distribution of microzooplancton (20-200 km)from the Río de la Plata Estuary, Argentina-Uruguay, SW Atlantic (36°S 56°W)were studied from samples collected during two oceanographic cruises at the end of austral spring (in 1999 and 2001)across a gradient from fluvial to coastal waters (200 km). Heterotrophic dinoflagellates, aloricate ciliates, tintinnids, radiolarians, rotifers and copepod nauplii were found. More than 110 taxa were registered, 35 were new records for the area. Three microzooplanktonic assemblages were distinguished using cluster analysis. Species and groups spatial distribution (horizontal and vertical)was related to the distribution of the maxima gradients (salinity, turbidity, etc.), estuarine circulation and water column mixing. The relative contribution of the different microzooplanktonic groups varied along the estuarine main axis in relation with changes in the hydrographic conditions, from tintinnids dominance in the inner estuary to a prevalence of aloricate ciliates and heterotrophic dinoflagellates in the middle and outer sectors. Those differences in the development of the groups would be related to the microzooplancton available resources according to environmental conditions in each case.
Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales (Argentina)
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