Rev. biol. mar. oceanogr. 49(3): 511-526

Article

Azadinium (Amphidomataceae, Dinophyceae) in the Southwest Atlantic: In situ and satellite observations

Rut Akselman¹, Rubén M. Negri¹ and Ezequiel Cozzolino¹

¹Instituto Nacional de Investigación y Desarrollo Pesquero, INIDEP, V. Ocampo 1, Escollera Norte, B7602HSA-Mar del Plata, Argentina

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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 (<1x10³ 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 (>10⁶ 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 growth. This bloom analyzed in situ, had satellite records from the SeaWiFS sensor which indicated high concentrations of chlorophyll-a (maximum of 11.76 mg Chlo-a m^-3) in a long and wide band (at least 2.5° latitude) near the continental shelf break and the Malvinas Current. It is still unknown if species of Azadinium are capable of synthesizing AZAs, a topic of interest in this region due to commercial bivalve exploitation.

Key words:  Azadinium, dinoflagellate blooms, SW Atlantic, SeaWiFS