HR: 08:30h
AN: OS21A-01 INVITED     [Abstracts]
TI: An Overview of Ecological Processes in the Rio de la Plata Estuary
AU: * Acha, M
EM: macha@inidep.edu.ar
AF: Instituto Nacional de Investigacion y Desarrollo Pesquero (INIDEP), Paseo Victoria Ocampo n§ 1, Mar del Plata, BA 7600 Argentina
AU: * Acha, M
EM: macha@inidep.edu.ar
AF: Universidad Nacional de Mar del Plata, Funes 3250, Mar del Plata, BA 7600 Argentina
AU: Mianzan, H
EM: hermes@inidep.edu.ar
AF: Instituto Nacional de Investigacion y Desarrollo Pesquero (INIDEP), Paseo Victoria Ocampo n§ 1, Mar del Plata, BA 7600 Argentina
AU: Mianzan, H
EM: hermes@inidep.edu.ar
AF: Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Rivadavia 1906, Buenos Aires, BA 1033 Argentina
AB: The Rio de la Plata, one of the most important estuarine environments in South America, is characterized by a salt-wedge regime. Large extension and shallow water depth make the estuary highly susceptible to atmospheric forcing. The estuary is a highly productive area, which sustain important artisanal and coastal fisheries in Uruguay and Argentina, mainly based on the whitemouth croaker, Micropogonias furnieri. The main goal of this paper is to summarize recent knowledge on this system, integrating physical, chemical and biological studies. This estuary is characterized by strong vertical salinity stratification, with marine waters (saltier and denser) penetrating deeper into the estuary along the bottom, while fresh waters advance ocean-ward on the surface, forming a salt wedge. The upstream reach of the salt wedge defines a bottom salinity fronts, whose location is controlled by the topography, a submerged shoal called Barra del Indio and at the opposite area, the convergence between the estuarine and marine waters define a surface salinity front. The convergence of water masses and the strong picnoclines at the head of the salt wedge produce the accumulation and retention of plankton, including the eggs of those fishes that concentrate here to spawn (e.g. Micropogonias furnieri and Brevoortia aurea) and even debris. High turbidity constrains here photosynthetic production and food chains are probably detritus based, supporting high densities of Acartia tonsa (Copepoda) and Neomysis americana (Mysid), both omnivorous species that complete its entire life-cycle within the estuary. In agreement, heterotophic microzooplankton is abundant. Moreover, high deposition of suspended matter support dense beds of the deposit feeding clams Mactra isabelleana. As soon as the water become less turbid, an extremely high chlorophyll signal is observed. The largest portion of the salt wedge regime (more than 200 km) is characterized by dense plankton aggregations below the picnocline, meanwhile the upper layer is biologically poor. Marine species penetrate the estuary advected or following the saline waters. The surface salinity front is the offshore end of the salt wedge. At this portion of the estuary, mixing of estuarine and marine waters and enhancement of vertical nutrient flux fertilize the frontal area and another maximum chlorophyll-a concentrations is observed. Zooplankton concentrations, mainly gelatinous plankton have been reported here. Reproduction of some fishes seem also associated to this surface front. This front is the more subtle and high dynamic portion of the wedge, showing a seasonal pattern driven by winds. It delineates the boundary between the estuary and the continental shelf waters. The influence of this large river in the ecological processes of the continental shelf is largely unknown. The knowledge on the ecology of the Rio de la Plata estuary has been remarkably enlarged during the last ten years, and some ongoing researches such as the study of different sources of primary production and the complexity of the trophic pathways, looks promissory and surely will contribute to the understanding of the regional importance of the estuary.
DE: 4235 Estuarine processes
DE: 4815 Ecosystems, structure and dynamics
DE: 4830 Higher marine organisms
DE: 4855 Plankton
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly