Polychaete Assemblages of Intertidal Mixohaline Flats of Bahía Samborombón (La Plata River Estuary-Argentina)

During November 1998- December 1999 period, a monthly benthic sample program was carried out along the intertidal flats of the southernmost part of Bahia Samborombon (external zone of La Plata River estuary). The main objectives of this study were to define the spatial and temporal distribution patterns of polychaete species in this mixohaline environment and to determinate the main environmental factors related with the distribution of these invertebrates. Two low diversity faunistic assemblages were identified in the studied area. One of them was related to muddy intertidal flats of San Clemente creek, characterized by its high clay and organic matter contents. The other assemblage was related to the sandy bottoms of Punta Rasa, an area with a higher marine influence, lower organic matter content and fine sand as the sediment dominant fraction. The first of these assemblages was dominated by Laeonereis culveri and presented as secondary species Heteromastus similis, Neanthes succinea, Nephtys fluviatilis and Scolecolepides sp.. The other assemblage had Laeonereis culveri as dominant species and Capitella capitata as subdominant member, being secondary species Heteromastus similis, Neanthes succinea, Polydora cornuta and Scolecolepides sp.. The polychaete assemblages of the studied area showed great affinities with other mixohalines coastal areas of Northern Buenos Aires Province and Southern Brazil