| Resumo: |
The distribution and abundance of mesozooplankton (specially copepod, cladoceran and appendicularian species) of the Buenos Aires shelf obtained in spring, during the years 2002, 2003 and 2004, were analysed. A small bongo net provided with 67 and 220 µm meshes, was employed in order to obtain a complete representation of the size spectrum of the mesozooplankton. The analysis included both the traditional optical method and the a new automatic image analysis (ZooImage). The results were related with the oceanographic conditions, which were, in general similar to the mean conditions for the study area. The finer mesh (67 µm) allowed a more accurate estimation of the abundance and biomass of small copepod species ( 1mm total length), producing the tick mesh (220 µm) more than 90 of underestimation for adults and/or development stages of dominant species like the copepods Oithona nana, Paracalanus parvus, Euterpina acutifrons and Parvocalanus in individuals with trunk length smaller than 600 µm. Small species dominated the area with non significant interannual differences of their abundance, in most of cases. Three faunistic areas were defined, which were characterized by key species. Acartia tonsa, P. crassirostris, P. parvus y Podon polyphemoides caracterized the Estuarine Area. O. nana, Microsetella norvegica, Evadne nordmanni y Oikopleura dioica, defined the Coastal Area, and the large copepods ( 1 mm of total length) such as Calanoides carinatus, Drepanopus forcipatus, Centropages brachiatus, Clausocalanus brevipes, Ctenocalanus vanus, and the cyclopoid O. helgolandica defined the Shelf Area. High abundance of potential zooplanktonic prey in sectors where highest densities of Engraulis anchoita larvae were recorded, allow to suppose that food is not limitant for larval growth and survival. ZooImage method, employed for the first time in the Argentine Sea, presented an accuracy similar to the traditional optical method for the abundance and biomass estimation of copepods and appendicularians. Due to the quicky obtention of results, this kind of analysis represent a very useful tool, adequate to the fisheries programs requirements.crassirostris. The underestimation of appendicularians abundance and biomass with the tick mesh was higher than 86 in individuals with trunk length smaller than 600 µm. Small species dominated the area with non significant interannual differences of their abundance, in most of cases. Three faunistic areas were defined, which were characterized by key species. Acartia tonsa, P. crassirostris, P. parvus y Podon polyphemoides caracterized the Estuarine Area. O. nana, Microsetella norvegica, Evadne nordmanni y Oikopleura dioica, defined the Coastal Area, and the large copepods ( 1 mm of total length) such as Calanoides carinatus, Drepanopus forcipatus, Centropages brachiatus, Clausocalanus brevipes, Ctenocalanus vanus, and the cyclopoid O. helgolandica defined the Shelf Area. High abundance of potential zooplanktonic prey in sectors where highest densities of Engraulis anchoita larvae were recorded, allow to suppose that food is not limitant for larval growth and survival. ZooImage method, employed for the first time in the Argentine Sea, presented an accuracy similar to the traditional optical method for the abundance and biomass estimation of copepods and appendicularians. Due to the quicky obtention of results, this kind of analysis represent a very useful tool, adequate to the fisheries programs requirements.
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