Distribución espacial del zooplancton del estuario del Río de la Plata: descripción sinóptica mediante la implementación de dos técnicas complementarias de muestreo.
Zooplankton plays a key role in the pelagic trophic chain, being the main source of food for fish larvae. Sizes of zooplanktonic organisms may vary in a very wide range, since micrometric organisms to large jellyfish. The high variability that usually characterizes the spatial distribution of zooplankton is related to both, biologic factors (reproduction, growth) and oceanographic factors (advection, water column stratification, etc) as well. Planktonic organisms are usually found associated to sharp oceanographic gradients, like termoclines or haloclines. These factors increase the difficulty to obtain synoptic descriptions of its patterns of spatial distribution. The main goal of this thesis was to produce a synoptic view of the spatial distribution of zooplankton in the Río de la Plata estuary. The Río de la Plata estuary is situated in a template zone of the South American coast (35° 00` S y 55° 30` W) (Fig. 1). Acoustic, oceanographic and zooplankton sampling were carried out along a transect of 140 nmi in length, performed in December 1999 along the axis of the estuary (Fig. 3). Continuous acoustic sampling was performed by means of a SIMRAD EY500 portable echosounder operating with a 120 kHz split beam transducer. Oceanographic and plankton sampling took place at stations located along the sailed transect. The transect was divided in three sectors: riverine, mixohaline and marine zones (Fig. 4). Values of volume backscattering were consistently lower for the riverine and marine zones (vertically homogeneous water column), compared with the mixohaline zone where the highest values (-65 dB) were recorded. A sharp salinity gradient (halocline) was observed in the mixohaline zone at 8 meters depth (Fig. 4). This was in coincidence with the highest values of sound backscattering, which ocuirred at the depth of the halocline. Three different types of sound scattering sources were considered in this analysis. The physical stratification of the water column (the halocline), the presence of sediments suspended and the scattering from planktonic organisms and nekton. It was hence concluded that the main source for the registered sound backscattering along the transect have to be associated to the presence of planktonic organisms and nekton. Each organism has a characteristic acoustic response. This is a function of size, shape, constitutive materials and orientation of the organisms in the water column. Planktonic organisms were grouped into functional groups depending on their characteristics. The following groups were identified : copepods, decapods larvae, holoplanctonic crustaceans, Scyphozoa (jellyfish), fish larvae without swimbladder (first ontogeny stages), and gas bearing fish larvae (Fig. 2). Correlation between observed and theoretical values are shown (Figures 8 to 13). Fish larvae, where present, resulted the most significative contribution to the total recorded scattering, seconded by copepods and holoplanktonic crustaceans. The Río de la Plata biotic is highly dynamic and occur over a large area, impossing real challenges to the methodology applyed to describe the abundance and spatial and temporal distribution of the inhabiting organisms. Acoustical techniques represent a powerful tool to obtain synoptic views of the present biota. For such dynamic areas, direct sampling methods as plankton net sampling has to be directed on the basis of both, oceanographic and acoustic information recorded in real time, and hence enabling for the best interpretation of the processes involving the biology of planktonic organisms.
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| Format: | Thesis/Dissertation biblioteca |
| Language: | Spanish / Castilian |
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Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales
2002
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| Subjects: | Estuarios, Dispersión de fondo, Ecosondas, Muestreo biológico, Zooplancton, Relevamientos ecoicos, Ictioplancton, Distribución geográfica, ASFA_2015::B::Backscatter, ASFA_2015::E::Echosounders, ASFA_2015::E::Estuaries, ASFA_2015::B::Biological sampling, ASFA_2015::Y::Zooplankton, ASFA_2015::E::Echo surveys, ASFA_2015::I::Ichthyoplankton, ASFA_2015::G::Geographical distribution, |
| Online Access: | http://hdl.handle.net/1834/11442 |
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