Resumen.-Los azaspirácidos (AZAs) son toxinas identificadas en invertebrados marinos y tienen amplia distribución geográfica, no reportadas aún en Argentina ni Uruguay. Aunque el primer agente causal identificado es el dinoflagelado fotosintético Azadinium spinosum, diversos estudios indican que otras especies sintetizan asimismo AZAs. Recientemente se ha detectado la presencia de A. cf. spinosum en el Atlántico Sudoccidental y la generación de dos extensas floraciones como nuevos eventos a escala global. En este estudio se analiza la distribución geográfica regional y desarrollo temporal de Azadinium así como las condiciones ecológicas de una tercera floración de A. cf. spinosum y su registro satelital. Azadinium presentó una amplia distribución que abarcó el norte de la plataforma de Argentina y sur de Uruguay, incluyendo la desembocadura del Río de la Plata, con abundancias generalmente bajas (<1x10 3 células L -1 ); un estudio en una estación de serie de tiempo mostró una marcada estacionalidad con mayores abundancias en primavera y otoño. La tercera floración (>10 6 células L -1 ) de A. cf. spinosum ocurrió en agosto-septiembre 1998 en un área coincidente con las previas, en condiciones hidrográficas propicias para su crecimiento poblacional. Esta floración comprobada in situ tuvo registros satelitales del sensor SeaWiFS que indicaron altas concentraciones de clorofila-a (máximo: 11,76 mg Clo-a m -3 ) dentro de una ancha y larga banda (al menos 2,5° de latitud) adyacente al talud continental y la Corriente de Malvinas. Aún desconocemos si las especies de Azadinium presentes en el Atlántico Sudoccidental son capaces de sintetizar AZAs, tema de interés debido a la explotación de bivalvos en bancos de profundidad.
Palabras clave: Azadinium, floraciones de dinoflagelados, Atlántico Sudoccidental, SeaWiFSAbstract.-Azaspiracid toxins (AZAs) have been identified in marine invertebrates and are of wide geographical distribution, but have not been reported in Argentina or Uruguay. The first identified causal agent is the photosynthetic dinoflagellate Azadinium spinosum, but new studies indicate that other species also synthesize AZAs. We have recently reported the presence of A. cf. spinosum in the Southwest Atlantic and the generation of two extended blooms as new global events. Here we analyze the ecological conditions of a third bloom of A. cf. spinosum and its satellite record, and report the regional distribution and temporal development of the genus Azadinium. Azadinium had a wide spatial distribution encompassing northern Argentine and southern Uruguayan shelves, including the mouth of the Río de la Plata. Abundance was generally low (<1x10 3 cells L -1 ), and analysis conducted at a time series station showed a marked seasonality in spring and autumn. A. cf. spinosum caused a third bloom and discolorations (>10 6 cells L -1 ) in August-September 1998 in the northern shelf of Argentina in an area that spatially coincided with the previous episodes, with hydrographic conditions propitious for its population gr...
The San Jorge Gulf, and the littoral to its north, is one of the most important fishing grounds for Argentina. Nevertheless, phytoplankton production has been scarcely studied. Here we analyzed during spring (2008) and summer (2009) the phytoplankton biomass, production, and the composition of phytoplankton and protozooplankton; their possible trophic relationships, and physical conditioners. At the south coast of the gulf during spring micro-nano-plankton (diatoms and dinoflagellates) were predominant and responsible for the maximum integrated production, comparable to that reported for the rich Argentinian shelf-break. Part of the organic carbon produced there was consumed by heterotrophic dinoflagellates, adding a trophic level to the food web. While at the center of the gulf, a conspicuous deep chlorophyll maximum would probably add organic matter to the bottom. During the following summer ( 2009), the ultrafraction represented the largest contribution to total phytoplankton biomass, and was dominated by Synechococcus sp. This, plus the abundance of ciliates, indicate the prevalence of a microbial food web during summer. It has been found that the frontal zones in the north and south of the gulf, favoring high phytoplankton biomass and its maintenance due to high primary production, provide a favorable food environment for impregnated female shrimp in spring, and for larvae during summer.
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