Distribución del plancton a mesoescala en un área de reproducción de la anchoíta en la plataforma bonaerense

Abstract

In order to determine the distribution patterns of phytoplanktonic and zooplanktonic species that constitute the main food of the argentine anchovy (Engraulis anchoita), a study was made within a coastal spawning area on meso-scaled space (approximately 7 miles between stations). It was observed the predominacne of the copepod Oithona helgolandica and copepodites stages of other small-sized species, thus inferring the preponderance of nauplii stages which constitute the main food of early anchovy larvae. A high spatial heterogeneity was found in the distrtibution of both phytoplanktonic and zooplanktonic communities. Phytoplankton showed a patchiness distribution both in horizontal and vertical directions. Diatoms, dinoflagellates and coccolithophoirids showed their own distribution patterns with biomass nuclei centered at different stations. The spatial distribution of the components within each taxonomic group seems to be of the contagious-type distribution. The positive correlation (r= 0,64*)as observed between immature stages of copepods and coccolithophorids seems to indicate a trophic direction of these consumers, which is also supported by the finding of coccolithophorids in copepods pellets. The phytoplankton crop as measured by population census and chlorophyll a concentrations (0,0-0,91 mg/m3)indicates an area of a low productive capacity.