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

Thalassas, 2004, 20 (2): 39-53 An International Journal of Marine Sciences

POLYCHAETE ASSEMBLAGES OF INTERTIDAL MIXOHALINE FLATS OF BAHÍA SAMBOROMBÓN (LA PLATA RIVER ESTUARY-ARGENTINA)

J. P. MARTIN(1,3), R. BASTIDA(1,2) & M. TRASSENS(1,2)

Keywords: polychaete, macrobenthos, tidal flats, estuaries, Bahía Samborombón , La Plata River.

ABSTRACT During November 1998- December 1999 period,a monthly benthic sample program was carried out along the intertidal flats of the southernmost part of Bahía Samborombón (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 ofthese 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 sedimentdominant 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 cornutaand 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 INTRODUCTION The coasts of the Buenos Aires province are characterized by two main environments: marine sandy beaches and mixohaline intertidal muddy flats. This last environment is mainly distributed along La PlataRiver estuary and Mar Chiquita coastal lagoon. There are also other less important estuarial areas as Bahía Blanca, Quequén Grande and Colorado rivers. The mixohaline intertidal flats play an important ecological role and are characterized by the presence of muddy-sandy sediments conforming beaches of low slope. The more extended ones are those present in the southernmost area of BahíaSamborombón, in
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(1) Depto. de Ciencias Marinas, Universidad Nacional de Mar del Plata, CC 43 (7600), Mar del Plata, Argentina, e-mail: martin_jpablo@yahoo.com.ar (2) Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) (3) Centro de Investigaciones de Puerto Deseado, Universidad Nacional de la Patagonia Austral, Puerto Deseado, Argentina

J. P. Martin, R. Bastida & M. Trassens

theexternal zone of La Plata River estuary. These intertidal flats have low water energy but great variability in relation with physical and chemical factors, and are inhabited by infaunal communities of low diversity (Ieno & Bastida, 1998). Among the few faunistic groups that conform these communities it can be mentioned decapods crustaceans and polychaetes. The first mixohaline polychaete studiesof Argentina were carried out in Mar Chiquita coastal lagoon by Olivier et al. (l972 a, 1972 b), and followed by Ieno & Elías (1995), Schwindt & Iribarne (2000), Palomo & Iribarne (2000), among others. The coastal polychaetes of Bahía Blanca were studied by Elías (1992a, 1992b), Elías & Ieno (1993) and Elías & Bremec (1994). More recently, polychaete communities of Río Quequén estuary were studiedby López Gappa et al. (2001).

Benthic invertebrates of intertidal flats, mainly polychaetes, are the most important trophic items of many resident and migratory fishes and birds of the mixohaline environments of the Buenos Aires province. In this way, energy is transferred from low trophic levels to higher ones (Olivier et al., 1972b; Ieno, 2000; Martin, 2002), being the top predators of...